delivered the opinion of the Court.
Section 510 of the Employee Retirement Income Security Act of 1974 (ERISA), 88 Stat. 895, makes it unlawful to *512 “discharge, fine, suspend, expel, discipline, or discriminate against a participant or beneficiary [of an employee benefit plan] for the purpose of interfering with the attainment of any right to which such participant may become entitled under the plan.” 29 U. S. C. § 1140. The Court of Appeals for the Ninth Circuit held that § 510 only prohibits interference with the attainment of rights that are capable of “vesting,” as that term is defined in ERISA. We disagree.
I
The individual petitioners are former employees of respondent Santa Fe Terminal Services, Inc. (SFTS), a wholly owned subsidiary of respondent The Atchison, Topeka and Santa Fe Railway Co. (ATSF), which was responsible for transferring cargo between railcars and trucks at ATSF’s Hobart Yard in Los Angeles, California. While petitioners were employed by SFTS, they were entitled to retirement benefits under the Railroad Retirement Act of 1974, 88 Stat. 1312, as amended, 45 U. S. C. § 231 et seq., and to pension, health, and welfare benefits under collective bargaining agreements involving SFTS and the Teamsters Union. SFTS provided its workers with pension, health, and welfare benefits through employee benefit plans subject to ERISA’s comprehensive regulations.
In January 1990, ATSF entered into a formal “Service Agreement” with SFTS to have SFTS do the same “inter-modal” work it had done at the Hobart Yard for the previous 15 years without a contract. Seven weeks later, ATSF exercised its right to terminate the newly formed agreement and opened up the Hobart Yard work for competitive bidding. Respondent In-Terminal Services (ITS) was the successful bidder, and SFTS employees who declined to continue employment with ITS were terminated. ITS, unlike SFTS, was not obligated to make contributions to the Railroad Retirement Account under the Railroad Retirement Act. ITS also provided fewer pension and welfare benefits under its
*513
collective bargaining agreement with the Teamsters Union than had SFTS. Workers who continued their employment with ITS “lost their Railroad Retirement Act benefits” and “suffered a substantial reduction in Teamsters benefits.”
Petitioners sued respondents SFTS, ATSF, and ITS in the United States District Court for the Central District of California, alleging that respondents had violated §510 of ERISA by “diseharg[ing]” petitioners “for the purpose of interfering with the attainment of . . . right[s] to which” they would have “become entitled” under the ERISA pension and welfare plans adopted pursuant to the SFTS-Teamsters collective bargaining agreement. See App. to Pet. for Cert. 29a, Complaint ¶ 33. Had SFTS remained their employer, petitioners contended, they would have been entitled to assert claims for benefits under the SFTS-Teamsters benefit plans, at least until the collective bargaining agreement that gave rise to those plans expired. The substitution of ITS for SFTS, however, precluded them from asserting those claims and relegated them to asserting claims under the less generous ITS-Teamsters benefit plans. According to petitioners, the substitution “interfer[ed] with the attainment” of their “right” to assert those claims and violated §510. Respondents moved to dismiss these §510 claims, and the District Court granted the motion.
The Court of Appeals for the Ninth Circuit affirmed in part and reversed in part.
II
The Court of Appeals’ holding that § 510 bars interference only with vested rights is contradicted by the plain language of § 510. As noted above, that section makes it unlawful to “discharge ... a [plan] participant or beneficiary ... for the purpose of interfering with the attainment of any right to which such participant may become entitled under the plan.” 29 U. S. C. § 1140 (emphasis added). ERISA defines a “plan” to include both “an employee welfare benefit plan [and] an employee pension benefit plan,” §1002(3), and specifically exempts “employee welfare benefit plants]” from its stringent vesting requirements, see § 1051(1). Because a “plan” includes an “employee welfare benefit plan,” and because welfare plans offer benefits that do not “vest” (at least insofar as ERISA is concerned), Congress’ use of the word “plan” in §510 all but forecloses the argument that §510’s interfer *515 ence clause applies only to “vested” rights. Had Congress intended to confine §510’s protection to “vested” rights, it could have easily substituted the term “pension plan,” see 29 U. S. C. § 1002(2), for “plan,” or the term “nonforfeitable” right, see §1002(19), for “any right.” But §510 draws no distinction between those rights that “vest” under ERISA and those that do not.
The right that an employer or plan sponsor may enjoy in some circumstances to unilaterally amend or eliminate its welfare benefit plan does not, as the Court of Appeals apparently thought, justify a departure from § 510’s plain language. It is true that ERISA itself “does not regulate the substantive content of welfare-benefit plans.”
Metropolitan Life Ins. Co.
v.
Massachusetts,
The flexibility an employer enjoys to amend or eliminate its welfare plan is not an accident; Congress recognized that “requir[ing] the vesting of these ancillary benefits would seriously complicate the administration and increase the cost of plans.” S. Rep. No. 93-383, p. 51 (1973). Giving employers this flexibility also encourages them to offer more generous benefits at the outset, since they are free to reduce benefits should economic conditions sour. If employers were locked into the plans they initially offered, “they would err initially on the side of omission.”
Heath
v.
Varity Corp.,
Respondents argue that the Court of Appeals’ decision must nevertheless be affirmed because §510, when applied to benefits that do not “vest,” only protects an employee’s right to cross the “threshold of eligibility” for welfare benefits. See Brief for Respondent Atchison, Topeka & Santa Fe Railway Co. et al. 18. In other words, argue respondents, *517 an employee who is eligible to receive benefits under an ERISA welfare benefit plan has already “attainted]” her “right[s]” under the plan, so that any subsequent actions taken by an employer cannot, by definition, “interfer[e]” with the “attainment of . . . right[s]” under the plan. According to respondents, petitioners were eligible to receive welfare benefits under the SFTS-Teamsters plan at the time they were discharged, so they cannot state a claim under §510. The Court of Appeals’ approach precluded it from evaluating this argument, and others presented to us, and we see no reason not to allow it the first opportunity to consider these-matters on remand.
We therefore vacate the judgment of the Court of Appeals and remand the case for further proceedings consistent with this opinion.
It is so ordered.
Notes
See
Shahid
v.
Ford Motor Co.,
