delivered the opinion of the Court.
This case presents the issue whether, in diversity actions, federal courts must apply a state statute that imposes a fixed penalty on appellants who obtain stays of judgment pending unsuccessful appeals.
I
Respondents brought this tort action in Alabama state court to recover damages for injuries sustained in a motorcycle accident. Petitioner removed the case to a Federal District Court having diversity jurisdiction. A jury trial resulted in a judgment of $800,000 for respondent Alan Woods and $5,000 for respondent Cara Woods. Petitioner posted bond to stay the judgment pending appeal, and the Court of Appeals affirmed without modification.
*3
Respondents then moved in the Court of Appeals, pursuant to Ala. Code § 12-22-72 (1986), for imposition of that State’s mandatory affirmance penalty of 10% of the amount of judgment. Petitioner challenged the application of this statute as violative of the equal protection and due process guarantees of the Fourteenth Amendment and as “a procedural rule . . . inapplicable in federal court under the doctrine of
Erie Railroad Company
v.
Tompkins,
We granted certiorari to consider the equal protection and due process challenges as well as the
Erie
claim.
l — l I — l
The Alabama statute provides in relevant part:
‘When a judgment or decree is entered or rendered for money, whether debt or damages, and the same has been stayed on appeal by the execution of bond, with surety, if the appellate court affirms the judgment of the court below, it must also enter judgment against all or any of the obligors on the bond for the amount of the affirmed judgment, 10 percent damages thereon and the costs of the appellate court. . . .” Ala. Code § 12-22-72 (1986). 1
*4
As set forth in the statute, then, a combination of three conditions will automatically trigger the 10% penalty: (1) the trial court must enter a money judgment or decree, (2) the judgment or decree must be stayed by the requisite bond,
2
and (3) the judgment or decree must be affirmed without substantial modification.
E. g., Chapman
v.
Rivers Construction Co.,
Petitioner contends that the statute’s underlying purposes and mandatory mode of operation conflict with the purposes and operation of Rule 38 of the Federal Rules of Appellate Procedure, and therefore that the statute should not be applied by federal courts sitting in diversity. Entitled “Damages for delay,” Rule 38 provides: “If the court of appeals shall determine that an appeal is frivolous, it may award just damages and single or double costs to the appellee.” See also 28 U. S. C. § 1912. Under this Rule, “damages are awarded by the court in its discretion in the case of a frivolous appeal as a matter of justice to the appellee and as a penalty against the appellant.” Advisory Committee’s Notes on Fed. Rule App. Proc. 38, 28 U. S. C. App., p. 492.
In
Hanna
v.
Plumer,
The constitutional constraints on the exercise of this rulemaking authority define a test of reasonableness. Rules regulating matters indisputably procedural are
a priori
constitutional. Rules regulating matters “which, though falling within the uncertain area between substance and procedure, are rationally capable of classification as either,” also satisfy this constitutional standard.
Id.,
at 472. The Rules Enabling Act, however, contains an additional requirement. The Federal Rule must not “abridge, enlarge or modify any substantive right. . . .” 28 U. S. C. §2072. The cardinal purpose of Congress in authorizing the development of a uniform and consistent system of rules governing federal practice and procedure suggests that Rules which incidentally affect litigants’ substantive rights do not violate this provision if reasonably necessary to maintain the integrity of that system of rules. See
Hanna, supra,
at 464-465;
Missis
*6
sippi Publishing Corp.
v.
Murphree,
Applying the
Hanna
analysis to an analogous Mississippi statute which provides for a mandatory affirmance penalty, the United States Court of Appeals for the Fifth Circuit concluded in
Affholder, Inc.
v.
Southern Rock, Inc.,
*7 We find the Fifth Circuit’s analysis persuasive. Rule 38 affords a court of appeals plenary discretion to assess “just damages” in order to penalize an appellant who takes a frivolous appeal and to compensate the injured appellee for the delay and added expense of defending the district court’s judgment. Thus, the Rule’s discretionary mode of operation unmistakably conflicts with the mandatory provision of Alabama’s affirmance penalty statute. Moreover, the purposes underlying the Rule are sufficiently coextensive with the asserted purposes of the Alabama statute to indicate that the Rule occupies the statute’s field of operation so as to preclude its application in federal diversity actions. 5
Respondents argue that, because Alabama has a similar Appellate Rule which may be applied in state court alongside the affirmance penalty statute, see Ala. Rule App. Proc. 38;
McAnnally
v.
Levco, Inc.,
Federal Rule 38 regulates matters which can reasonably be classified as procedural, thereby satisfying the constitutional standard for validity. Its displacement of the Alabama statute also satisfies the statutory constraints of the Rules Enabling Act. The choice made by the drafters of the Federal Rules in favor of a discretionary procedure affects only the process of enforcing litigants’ rights and not the rights themselves.
Ill
We therefore hold that the Alabama mandatory affirmance penalty statute has no application to judgments entered by federal courts sitting in diversity.
Reversed.
Notes
Compare Ky. Rev. Stat. §26A.300 (1985) (mandatory 10% penalty for second appeal); Miss. Code Ann. § 11-3-23 (Supp. 1986) (15% mandatory penalty regardless of stay); Va. Code § 16.1-113 (Supp. 1986) (10% mandatory penalty regardless of stay).
Under Alabama law, an appellant may obtain a stay of judgment pending appeal by providing an acceptable surety bond of a set amount, which in this case would have been 126% of the trial court’s judgment had the case been tried in state court. Ala. Rule App. Proc. 8(a)(1).
Article III of the Constitution, augmented by the Necessary and Proper Clause of Article I, § 8, cl. 18, empowers Congress to establish a system of federal district and appellate courts and, impliedly, to establish procedural Rules governing litigation in these courts. In the Rules Enabling Act, Congress authorized this Court to prescribe uniform Rules to govern the “practice and procedure” of the federal district courts and courts of appeals. 28 U. S. C. § 2072. Though
Hanna
v.
Plumer,
The Mississippi statute applies without regard to whether the judgment has been stayed pending appeal. Miss. Code Ann. § 11-3-23 (Supp. 1986). In
Walters
v.
Inexco Oil Co.,
Rule 37 of the Federal Rules of Appellate Procedure provides further indication that the Rules occupy the Alabama statute’s field of operation so as to preclude its application in diversity actions. Since the affirmance penalty only applies if a trial court’s judgment is stayed pending appeal, see Ala. Code § 12-22-72 (1986), it operates to compensate a victorious ap-pellee for the lost use of the judgment proceeds during the period of appeal. Federal Rule 37, however, already serves this purpose by providing for an award of postjudgment interest following an unsuccessful appeal. See also 28 U. S. C. § 1961.
In addition, we note that federal provisions governing the availability of a stay of judgment pending appeal do not condition the procurement of a stay on exposure to payment of any additional damages in the event the appeal is unsuccessful and, unlike the state provision in this case, allow the federal courts to set the amount of security in their discretion. Compare Fed. Rules Civ. Proc. 62(d) and 62(g) and Fed. Rule App. Proc. 8(b) with Ala. Rule App. Proc. 8(b). See also 28 U. S. C. § 1651.
