OPINION
This appeal presents three issues related to the federal preemption of state causes of action. Plaintiff-appellant Stacy Hoik brought several state law claims against defendant-appellee the Snapple Beverage Corporation in the Superior Court of New Jersey. After removing Hoik’s lawsuit to the United States District Court for the District of New Jersey, Snapple sought to dismiss Hoik’s complaint on, inter alia, the grounds of express preemption, implied field preemption, and implied conflict preemption. The District Court granted Snapple’s motion on the basis of implied preemption. For the reasons discussed below, we will reverse.
I.
A.
Congress has regulated food and beverage labeling for more than 100 years. In 1906, it passed legislation commonly known as the “Wiley Act” that established labeling standards. Pure Food and Drug Act of 1906, Pub.L. No. 59-384, 34 Stat. 768, repealed by Act of June 25, 1938, ch. 675, § 902(a), 52 Stat. 1059. At the time, the Wiley Act was considered a substantial reform because it prohibited the adulteration and misbranding of food sold and distributed in interstate commerce. Pub.L. No. 59-384, §§ 7-8. By today’s standards, however, the Wiley Act offered only modest reforms: it “enabled the Government to go to court against illegal products but lacked affirmative requirements to guide compliance. Labels were not even required to state the weight or measure— only that a contents statement, if used, must be truthful.” U.S. Food and Drug Administration, The Story of the Laws Behind the Labels, Part II (1981).
Congress replaced the Wiley Act in 1938 with the Federal Food, Drug, and Cosmetic Act (“FDCA”). Pub.L. No. 75-717, 52 Stat. 1040 (1938). Mounting public com cern over unsafe food and drug products and marketing prompted its passage.
United States v. Bhutani,
In response to growing concerns from consumer groups about unsubstantiated health claims on food and beverages, the FDA and Congress began considering a national labeling law. Claudia L. Andre, Note, What’s in that Guacamole? How Bates and the Power of Preemption Will Affect Litigation Against the Food Industry, 15 Geo. Mason L.Rev. 227, 232 (2007). In 1990, Congress passed the Nutrition Labeling and Education Act (“NLEA”). Pub.L. No. 101-535, 104 Stat. 2353 (1990) (codified at 21 U.S.C. § 343 et seq.). NLEA introduced a number of substantial reforms: (1) it required nutrition labeling for nearly all food products under the authority of the FDA, with exemptions for small businesses, restaurants, and some other retail establishments; (2) it changed the requirements for ingredient labels on food packages; (3) it imposed and regulated health claims on packages; (4) it standardized all nutrient content claims; and (5) it standardized serving sizes. The Impact of the Nutrition Labeling and Education Act of 1990 on the Food Industry, 47 Admin. L.Rev. 605, 606 (1995).
B.
Snapple Beverage Corporation (“Snapple”) manufactures a variety of beverages, including a number of juice and tea-based drinks. In its marketing and advertising materials, Snapple represents that these beverages are “All Natural.” As the FDA has acknowledged, “[t]he word ‘natural’ is often used to convey that a food is composed only of substances that are not man-made and is, therefore, somehow more wholesome.” Food Labeling: Nutrient Content Claims, General Principles, Petitions, Definition of Terms, 56 Fed.Reg. 60,421, 60,466 (Nov. 27, 1991). Snapple products, however, contained high fructose corn syrup (“HFCS”), an ingredient manufactured from processed cornstarch. 1
Stacy Hoik bought two bottles of Snapple on May 4, 2007. She paid $1.09 for each bottle. She had purchased other Snapple products over the preceding six years. Hoik contends that the labels on these products are deceptive. She argues that consumers “have been, and continue to be, easy prey for Snapple’s unlawful activities because of their willingness to pay a premium price for foods and beverages, including Snapple beverages, that are represented to be ‘All Natural.’ ”
C.
Hoik filed a class action lawsuit against Snapple in the Superior Court of New Jersey, asserting claims on the basis of: (I) the New Jersey Consumer Fraud Act; (II) unjust enrichment and common law restitution; (III) breach of express warranty; and (IV) breach of the implied warranty of merchantability. Hoik’s claims were predicated on her belief that a number of statements on Snapple’s labels were misleading. She argued that (1) Snapple products were not “All Natural” because they contained HFCS; (2) Snapple products were not “Made from the Best Stuff on Earth,” as indicated on the label; and (3) Snapple falsely labeled some beverages, for example, calling one drink “Aeai *333 Blackberry Juice,” despite the fact that the drink contained neither acai berry juice nor blackberry juice.
Snapple removed the case to the United States District Court for the District of New Jersey pursuant to the Class Action Fairness Act, 28 U.S.C. 1453(b). It then filed a motion to dismiss. The parties subsequently agreed that Hoik could amend her complaint, rather than respond to Snapple’s motion. In October 2007, Hoik filed an Amended Complaint, which reasserted that Snapple’s labels were misleading because they claimed the products were “All Natural” and because Snapple advertised some products as containing juice that was not in the beverages. The Amended Complaint did not allege any claims based on Snapple’s use of the phrase “Made From the Best Stuff on Earth.” Snapple filed a second motion to dismiss, arguing that Hoik’s claims were preempted, that the claims should be dismissed under the doctrine of primary jurisdiction, and that the allegations failed to state a claim. Hoik responded by dropping the argument related to the juice components of Snapple beverages, leaving only the claim that Snapple products containing HFCS were deceptively labeled “All Natural.”
The District Court heard oral argument on Snapple’s motion to dismiss in June 2008. On June 12, 2008, the District Court dismissed Hoik’s complaint. It held that Snapple’s claims were preempted. In its opinion, the District Court correctly identified and discussed the three types of preemption. It also noted that Snapple argued that all three types of preemption were present in this case, as Snapple contended that (1) NLEA expressly preempted state labeling requirements that are not identical to federal requirements; (2) the comprehensive nature of the FDCA and its implementing regulations demonstrate that Congress intended the federal government to occupy the field; and (3) that state law stands as an obstacle to the purposes underlying the FDCA. Next, the District Court rejected Snapple’s express preemption argument, stating that there was not “specific preemptive language” in the FDCA that covered the claims. Nonetheless, the Court ruled that “Plaintiffs claims in this case are impliedly preempted by the detailed and extensive regulatory scheme established by the [FDCA] and the FDA’s implementing regulations.”
The District Court stated that the FDA has used the broad authority granted to it under the FDCA to issue comprehensive regulations governing the labeling and naming of juice drinks. The Court declared that the comprehensive nature of these regulations demonstrate that “the FDA has carefully balanced beverage industry and consumer interests and created a complex regulatory framework to govern beverage labeling.” Though it acknowledged that the FDA has not defined “natural,” it found that the “FDA has in fact contemplated the appropriate use of the term,” as indicated by the FDA’s definition of “natural flavor” and its informal policy regarding use of the term “natural.” The Court also noted that the FDA has the authority to enforce the FDCA and regulations issued pursuant to it. In the Court’s view, these factors counseled in favor of its conclusion “that the [FDCA] and FDA regulations so thoroughly occupy the field of beverage labeling at issue in this case that it would be unreasonable to infer that Congress intended states to supplement this area.”
Finally, the District Court deferred to the agency’s expertise in the regulation of food and beverages. It asserted that it would be inappropriate for the Court to set rules, which the FDA “with all of its scientific expertise” has not yet done. Thus, *334 the District Court concluded that the claims were “impliedly preempted” because “permitting states through statutes or common law causes of action to impose additional limitations and requirements on beverage labels such as described here would create obstacles to the accomplishment of Congress’s objectives. 2
Hoik filed this timely appeal.
II.
The District Court had jurisdiction under 28 U.S.C. § 1332(d), the Class Action Fairness Act. This Court has jurisdiction pursuant to 28 U.S.C. § 1291. Our review of a district court’s ruling on a motion to dismiss is plenary.
Evancho v. Fisher,
III.
Snapple argues that the District Court’s dismissal must be upheld “whether analyzed under the doctrine of express preemption, implied ‘field’ preemption, or implied ‘obstacle’ preemption.” The preemption doctrine is rooted in Article VI of the United States Constitution, which states that the laws of the United States “shall be the supreme Law of the Land; ... any Thing in the Constitution or Laws of any State to the Contrary notwithstanding.” U.S. Const, art. VI, cl. 2. Under the Supremacy Clause, federal law may be held to preempt state law where any of the three forms of preemption doctrine may be properly applied: express preemption, field preemption, and implied conflict preemption.
Hillsborough County, Fla., v. Automated Med. Labs., Inc.,
Additionally, we must begin our analysis by applying a presumption against preemption.
Cipollone v. Liggett Group, Inc.,
Health and safety issues have traditionally fallen within the province of state regulation. This is true of the regulation of food and beverage labeling and branding.
Plumley v. Massachusetts,
A.
Snapple argues that Hoik’s state law claims are expressly preempted by NLEA, specifically 21 U.S.C. § 343-1(a)(3). As a threshold matter, however, we must consider whether this issue is properly before üs. As stated above, Hoik initially argued that Snapple’s labels were misleading on several grounds, namely because Snapple claimed the products were “All Natural” despite containing HFCS and because Snapple advertised some products as containing juice that was not in the beverages. Hoik subsequently dropped the argument related to the juice contents of certain Snapple beverages. This prompted Snapple to concede, during oral argument before the District Court, that it was no longer arguing express preemption: “[T]here’s only one preemption argument left because of the dropping of the juice claims — There was expressed [sic] preemption, there was implied field preemption, and now there’s implied obstacle preemption. And it’s implied obstacle preemption that applies to the high fructose corn syrup natural claims.” Yet, on appeal, Snapple again raises express preemption.
Hoik argues that because Snapple did not raise express preemption before the District Court in relation to her HFCS argument, Snapple has waived its express preemption argument. Snapple counters that “[w]here a new ground would support affirmance, this Court may invoke it so long as it is supported by the record.”
First, we note that the District Court did not rule in Snapple’s favor on express preemption. The Court stated that it “agrees with Plaintiff that Congress has not explicitly preempted Plaintiffs claims by inserting any specific preemptive language into the [FDCA]----” It also noted that “Snapple’s express preemption arguments were directed at Plaintiffs claims concerning the fruit juices contained in Snapple beverages, which Plaintiff has withdrawn.” Because the District Court did not rule in Snapple’s favor on its express preemption argument, we do not have an express preemption claim to affirm.
Second, Snapple is correct that this Court has held that “we may affirm a correct decision of the district court on grounds other than those relied upon by the district court.”
Cent. Pa. Teamsters Pension Fund v. McCormick Dray Line Inc.,
We conclude that Snapple has waived its express preemption argument with regard to Hoik’s HFCS claims. Though Snapple contended in its two motions to dismiss that Hoik’s juice content claims were expressly preempted by 21 U.S.C. § 343-1(a)(3), it did not raise this provision with regard to Hoik’s HFCS claim. In fact, it did not raise any express preemption argument in response to the HFCS claim and explicitly disclaimed the applicability of express preemption to this claim. This clearly demonstrates that the issue was not before the District Court. For this reason, we conclude that the issue is waived. 3
B.
Field preemption occurs when state law occupies a “field reserved for federal regulation,” leaving no room for state regulation.
United States v. Locke,
First, we note that NLEA declares that courts may not find implied preemption based on any provision of NLEA. It states that the Act “shall not be construed to preempt any provision of State law, unless such provision is expressly preempted under [21 U.S.C. § 343-1] of the Federal Food, Drug, and Cosmetic Act.” Pub.L. No. 101-535, § 6(c)(1). Accordingly, if we are to find that Hoik’s claims are impliedly preempted, we must do so based on provisions of federal law other than NLEA. 4
*337 Given this limitation, Snapple argues that the FDCA, preNLEA, broadly addressed labeling and the misbranding of food and beverage products. 5 Snapple has also argued, both in its brief and during oral argument, that the FDA has promulgated, pursuant to its authority under the FDCA, “exhaustive” regulations regarding juice products in particular. Finally, Snapple asserts that the FDA has addressed HFCS and declared it to be “natural.” Snapple submits that “[fjederal law thus comprehensively regulates misbranding of food in general, juice beverages in particular, the distinction between natural and artificial, and even the specific question of whether HFCS can be ‘natural.’ ” For this reason, Snapple maintains that the District Court’s analysis was correct.
Hoik argues that the field in this case is not juice regulation, but rather food and beverage labeling. She contends that NLEA forecloses the implied preemption of state law in the food and beverage field. She reasons that the limited nature of the express preemption provision in NLEA, which applies only to those federal laws specifically enumerated, “would serve no purpose and would simply be surplus if Congress had intended to occupy the entire field of food and beverage labeling.” She also cites NLEA’s legislative history to demonstrate that Congress intended to preserve state authority in the food and beverage labeling field.
As discussed briefly above, field preemption requires a demonstration that “Congress ... left no room for state regulation of these matters.”
Locke,
Second, as Hoik argues, NLEA’s express preemption provision demonstrated that Congress recognized the existence of state laws relating to beverages generally and juice products specifically.
See, e.g.,
21 U.S.C. § 343-l(a)(2) (preempting state laws that conflict,
inter alia,
with federal law requiring foods to indicate: (1) the name and location of the manufacturer, as well as the weight or quantity of food contained in a package; and (2) the percentage of fruit or vegetable juice contained in a beverage). NLEA plainly states that the Act “shall not be construed to preempt any provision of State law, unless such provision is expressly preempted under [21 U.S.C. § 343-1] of the Federal Food, Drug, and Cosmetic Act.” Pub.L. No. 101-535, § 6(c)(1). Furthermore, NLEA declares that its express preemption provision “shall not be construed to apply to any requirement respecting a statement in the labeling of food that provides for a warning concerning the safety of the food or component of the food,” thereby preserving state warning laws. Pub.L. No. 101-535, § 6(c)(2). These provisions demonstrate that Congress was cognizant of, the operation of state law and state regulation in the food and beverage field, and it therefore enacted limited exceptions in NLEA. As the Supreme Court instructed in
Levine, “
‘[t]he case for federal pre-emption is particularly weak where Congress has indicated its awareness of the operation of state law in a field of federal interest, and has nonetheless decided to stand by both concepts and to tolerate whatever tension there [is] between them.’ ”
Furthermore, we note that the FDA has stated that it does not intend to occupy the field of food and beverage labeling, even with regard to regulations affecting juice products.
See Levine,
The preemption issue is complex and divisive: whether a uniform, national label is necessary for consumers and manufacturers to function in the marketplace versus whether States should be *339 permitted to require additional information for their residents. The input of States, as well as consumers, businesses, and other concerned parties is essential in evaluating this matter. FDA therefore requests comment on the issue of whether preemption is appropriate.
Food Labeling; Mandatory Status of Nutrition Labeling and Nutrient Content Revision, 55 Fed.Reg. at 29,509; Food Labeling; Serving Sizes, 55 Fed.Reg. at 29,528.
Finally, we are reluctant to find field preemption predicated solely on the comprehensiveness of federal regulations. The Supreme Court has repeatedly stated that “the mere existence of a federal regulatory scheme,” even a particularly detailed one, “does not by itself imply preemption of state remedies.”
English,
In the instant case, not only do we lack a “clear and manifest” statement from Congress of its intent to preempt, but we also note that the claims in this case are governed by the presumption against preemption. These factors, along with the Supreme Court’s direction that we should not infer field preemption from the comprehensiveness of a regulatory scheme alone, lead us to conclude that neither Congress nor the FDA intended to occupy the fields of food and beverage labeling and juice products.
C.
Implied conflict preemption is present when it is “impossible for a private party to comply with both state and federal requirements.”
English,
Snapple submits that Hoik’s claims are preempted because they stand as an obstacle to federal law. It contends that the FDA has adopted a policy regarding the use of the term “natural” and that this policy would be undermined by Hoik’s suit, Specifically, it alleges that liability in Hoik’s suit would result in the imposition of “additional conditions not contemplated by the federal regime.” Additionally, Snapple argues that state law must yield if it undermines federal efforts to create uniform standards.
Hoik counters that her state causes of action do not serve as an obstacle to federal objectives because there “are no federal *340 requirements in place regarding the term ‘natural.’ ” She also asserts that her claims do not conflict with federal law because, even if she obtained a favorable verdict, Snapple would not be required to undertake a specific corrective action.
To determine whether Hoik’s claims present an obstacle to federal law, we must as an initial matter consider whether the FDA has regulations or has otherwise taken actions that are capable of having preemptive effect. In
Fellner v. Tri-Union Seafoods, L.L.C.,
we declared “that it is federal
law
which preempts contrary state law; nothing short of federal law can have that effect.”
In determining whether an agency action is entitled to deference, we will be guided by the Supreme Court’s pronouncement that “ ‘[i]t is fair to assume generally that Congress contemplates administrative action with the effect of law when it provides for a relatively formal administrative procedure tending to foster the fairness and deliberation that should underlie a pronouncement of such force.’ ”
Id.
(quoting
United States v. Mead Corp.,
In this case, we must determine whether the FDA’s policy statement on the use of the word “natural” has preemptive effect. In 1991, the FDA announced that it was considering defining the term “natural” for the purpose of future rulemaking. Food Labeling: Nutrient Content Claims, General Principles, Petitions, Definition of Terms, 56 Fed.Reg. 60,421, 60,466 (Nov. 27, 1991). At that time, the FDA recounted its existing “informal policy” on the use of the term:
[T]he agency has considered “natural” to mean that nothing artificial or synthetic (including colors regardless of source) is included in, or has been added to, the product that would not normally be expected to be there. For example, the addition of beet juice to lemonade to make it pink would preclude the product being called “natural.”
Id. (emphasis added).
We conclude that the FDA’s policy statement regarding use of the term “natural” is not entitled to preemptive effect. First, the FDA declined to adopt a formal definition of the term “natural.” After soliciting comments on the use of the term “natural,” the FDA recognized that the use of the term “is of considerable interest to consumers and industry.” Food Labeling: Nutrient Content Claims, General Principles, Petitions, Definition of Terms; Definitions of Nutrient Content
*341
Claims for the Fat, Fatty Acid, and Cholesterol Content of Food, 58 Fed.Reg. 2,302, 2,397 (Jan. 6, 1993). It also stated that it believed “that if the term ‘natural’ is adequately defined, the ambiguity surrounding use of this term that results in misleading claims could be abated.”
Id.
Nevertheless, the FDA declined to do so: “Because of resource limitations and other agency priorities, FDA is not undertaking rulemaking to establish a definition for ‘natural’ at this time.”
Id.
This hardly supports preemption.
See Sprietsma v. Mercury Marine,
Though the FDA declined to adopt a formal definition of “natural,” it declared that it would continue to adhere to the informal policy previously announced. Food Labeling: Nutrient Content Claims, General Principles, Petitions, Definition of Terms; Definitions of Nutrient Content Claims for the Fat, Fatty Acid, and Cholesterol Content of Food, 58 Fed.Reg. at 2,397. This too, however, lacks preemptive weight. The FDA’s request for comments on use of the term “natural” makes clear that the FDA’s informal policy predated the request for notice and comment. Food Labeling: Nutrient Content Claims, General Principles, Petitions, Definition of Terms, 56 Fed.Reg. at 60,466. Because a search of the Federal Register results in neither earlier references to this policy nor other requests for comments on the use of the term “natural,” the record demonstrates that the FDA arrived at its policy without the benefit of public input. Additionally, after requesting comments on the use of the term “natural,” the FDA did not appear to consider all the comments received. For instance, the FDA noted that one comment questioned whether restrictions on the use of “natural” could raise First Amendment concerns. Food Labeling: Nutrient Content Claims, General Principles, Petitions, Definition of Terms; Definitions of Nutrient Content Claims for the Fat, Fatty Acid, and Cholesterol Content of Food, 58 Fed.Reg. at 2,397. The FDA did not respond to this comment, as it declared it moot in light of its decision not to proceed with a definition. Id. In fact, despite numerous public comments, the FDA announced that it would adhere to its preexisting policy on the use of the term “natural” and make no changes. Id. at 2,407. Finally, the FDA stated that it was declining to define “natural,” in part, because there were still “many facets of the issue that the agency will have to carefully consider if it undertakes a rule-making to define the term ‘natural.’ ” Id. This statement alone demonstrates a lack of the kind of “fairness and deliberation” contemplated by Fellner.
Despite these shortcomings, Snapple argues that the FDA’s policy is entitled to preemptive effect because the FDA has enforced the informal policy. In its briefs to this Court, Snapple directed our attention to several letters in which the FDA told a food or beverage manufacturer to remove the term “natural” from one of its labels for violating the FDA policy on the use of the term “natural.” We do not think these letters are sufficient to accord the policy the weight of federal law. In
Fellner,
we recognized that Congress likely intended to give administrative action the effect of law when the agency adhered to “a relatively formal administrative procedure tending to foster the fairness and deliberation that should underlie a pronouncement of such force.’ ”
We believe that neither the FDA policy statement regarding the use of the term “natural” nor the FDA’s letter indicating that some forms of HFCS may be classified as “natural” have the force of law required to preempt conflicting state law. Both lack the formal, deliberative process contemplated in Fellner. As a result, there is no conflict in this ease because there is no FDA policy with which state law could conflict.
IV.
For the reasons discussed above, we conclude that Hoik’s claims are not preempted. We will reverse the judgment of the District Court, and remand to the District Court for further proceedings consistent with the foregoing opinion.
Notes
. At the time of Hoik's suit, Snapple products contained HFCS. In late 2008, Snapple announced that it was reformulating its lineup of beverages and replacing HFCS with sugar in its beverages. See, e.g., Betsy McKay, Snapple Introduces Snappier Look, New Formula-Beverage Brand to Emphasize Tea's Health Benefits Amid Weaker U.S. Sales; Sugar Will Be Added to Improve Drinlcs’ Flavor, Wall St. J„ Nov. 14, 2008, at B4.
. Because the District Court found that Hoik's claims were preempted, it did not address Snapple’s primary jurisdiction argument or whether Hoik's complaint stated a claim for relief under New Jersey law.
. Because we find that Snapple has waived its express preemption argument, we will not reach the merits of this issue. However, we note that the FDA appears to consider HFCS a sweetener and not a flavoring, and thus the allegedly troublesome federal statute, § 343 (k), would be inapplicable. See, e.g., 21 C.F.R. § 184.1866; .Committee on Food Chemicals Codex, Institute of Medicine, Food Chemical Codex 191-92 (4th ed.1996). Additionally, § 343 (k) is a disclosure require ment — i.e., it regulates only what companies must place on a label. Hoik's claims go to what a company cannot put on a label for the purposes of commercial marketing, an important distinction.
. NLEA expressly preserves implied preemption claims based on other provisions of fed *337 eral law. It states that the provision prohibiting implied preemption based on NLEA:
shall not be construed to affect preemption, express or implied, of any such requirement of a State or political subdivision, which may arise under the Constitution, any provision of the Federal Food, Drug, and Cosmetic Act not amended by [NLEA’s preemption provision subsection], any other Federal law, or any Federal regulation, order, or other final agency action....
Pub.L. No. 101-535, § 6(c)(3).
. Though Snapple raised field preemption in its memorandum in support of its motion to dismiss the plaintiff’s amended complaint, and this argument was not particularized to Hoik's juice claims, Snapple disavowed the application of field preemption to Hoik’s HFCS claim during oral argument before the District Court. Nevertheless, Hoik has not put Snapple’s oral argument waiver before us.
We have held that "[a]n issue is waived unless a party raises it in its opening brief, and for those purposes a passing reference to an issue ... will not suffice to bring that issue before this court.”
Laborers’ Int’l Union v. Foster Wheeler Corp.,
. We also reject Snapple’s arguments that a letter from a FDA official from July 2008 is entitled to weight. The letter was not issued as part of any formal rulemaking or adjudication and was not subject to notice and comment. Additionally, the FDA issued the letter in response to a question from interested parties, rather than doing so in an enforcement action. Under
Fellner,
this letter does not have the force of law — it lacks the relatively formal procedure and “fairness and deliberation” to suggest that Congress intended this agency action "to be a binding and exclusive application of federal law.”
Fellner,
Furthermore, despite Snapple’s assertions, the letter is not entitled to deference as an agency's interpretations of its regulations. Though the FDA letter regarding HFCS referenced the regulation pertaining to flavoring, the FDA letter did not state that it either interpreted or applied this regulation when it considered whether HFCS was “natural.”
