OPINION OF THE COURT
WEIS, Circuit Judge.Plaintiffs filed suit in the district court asserting that their involuntary retirements in 1975 and 1976 before they reached the age of 65 violated the Age Discrimination in Employment Act of 1967, 29 U.S.C. §§ 621— 634 (1976)(ADEA). The court entered summary judgment for the defendant on that count but ordered a trial on other allegations of discrimination. In 1978, after entry of the summary judgment, Congress revised the ADEA to prohibit forced retirement under age 70 in most situations. Plaintiffs contend on appeal that the amendments control our disposition of this case. We conclude that the amendments do not apply to a retirement that occurred before the effective date of the enactment, but remand for a determination of whether the defendant’s pension plan was bona fide and not a subterfuge.
Plaintiffs Honeiser and Kalmbach were employees of defendant American Can Company until they were involuntarily retired. Honeiser began working for the company on March 16,1964, and on September 1 of that year he voluntarily joined the company retirement plan for salaried employees. He was 56 years old on January 1, 1976, the date of his retirement, when he became eligible for a pension of $194.92 per month for life. Before retirement he had been earning $1,706.00 per month.
Kalmbach began his employment with the defendant on December 3, 1962, joined the plan on July 1, 1963, and was age 61 in September 1975 when he was retired on a monthly pension of $215.91. His salary in September 1975 amounted to $1,511.00 per month.1
The American Can retirement plan was established on July 1, 1959 and covered, on a voluntary basis, all regularly employed full-time salaried employees except those covered by a collective bargaining agreement. From July 1, 1959 until December 31, 1971, the benefits provided for retirement before the plan’s normal age of 65 were computed on the basis of a member’s salary and contributions. Employee contributions were eliminated after January 1, 1972 and thereafter early retirement pensions were based on salary and years of service. The plan was amended again on January 1, 1974 to provide a different formula for early retirement benefits. Under this arrangement, unless the employee had reached age 55 and completed 30 years of accredited service, his pension could be reduced by one fourth of 1% for each month by which his early retirement preceded his “normal retirement date” at age 65. Generally the plan allowed for early retirement at any time between ages 55 and 65 at the option of either the company or the employee.
Dissatisfied with their involuntary retirement from the company, the plaintiffs first exhausted administrative remedies and then filed suit on December 21, 1976, alleging that they had been forced into retirement in violation of the ADEA. They sought reinstatement as well as damages. Plaintiffs later amended the complaint to assert that they were also denied merit and *1119other salary increases because of age. The defendant moved for summary judgment on the ground that the plaintiffs had been retired pursuant to a bona fide pension plan and were not, therefore, covered by the ADEA. 29 U.S.C. § 623(f)(2) (1976).2 The parties agreed upon the material facts, although the plaintiff contended that the plan was a subterfuge and was not bona fide.
The district judge distinguished United Air Lines, Inc. v. McMann, 434 U.S. 192, 98 S.Ct. 444, 54 L.Ed.2d 402 (1977), which upheld certain forced retirements under the 1967 Act, on the ground that they were mandated by a bona fide plan. But he found Zinger v. Blanchette, 549 F.2d 901 (3d Cir. 1977), cert. denied, 434 U.S. 1008, 98 S.Ct. 717, 54 L.Ed.2d 750 (1978), which allowed retirements on an adequate pension under a discretionary plan, controlling. Thus he granted summary judgment on the retirement claims but left open the claims of discrimination in deprivation of merit raises. Without discussion or findings of fact, the court concluded that the plan was bona fide. Judgment was entered on March 20, 1978.
A few weeks later, on April 6, 1978, the same day that plaintiffs took this appeal,3 Congress revised the ADEA to specifically prohibit involuntary retirement because of age, the amendments to be effective upon enactment.4 On appeal, plaintiffs contend that the 1978 amendments should apply to this case even though the retirements at issue took place before the effective date of the legislation. In this contention, the plaintiffs are joined by the Secretary of Labor, who has filed an amicus brief.
The retroactivity of legislation has been a frequent subject of litigation in the statutory construction field, not only in common law countries but in other civilizations as well. In his frequently cited article, The Rule Against Retroactive Legislation: A Basic Principle of Jurisprudence, 20 Minn.L.Rev. 775 (1936), E. E. Smead observed that the “bias against retroactive laws is an ancient one” and reviewed classical Greek and Roman examples. Id. at 775. The broad generalization, however, has been extensively narrowed over time and may no longer be relied upon in all circumstances. For example, modifications in procedural law are generally given effect in cases where the subject matter is restricted to events that occurred before the statutory enactment. Grummitt v. Sturgeon Bay Winter Sports Club, 354 F.2d 564 (7th Cir. 1965). In some instances, legislation that affected the substantive rights of parties to a prior transaction has been enforced. See Home Building & Loan Association v. Blaisdell, 290 U.S. 398, 54 S.Ct. 231, 78 L.Ed. 413 (1934). See generally Hochman, The Supreme Court and the Constitutionality of Retroactive Legislation, 73 Harv.L.Rev. 692 (1960).
*1120The immediate application of substantive legislation to pending cases is a form of retroactivity that at times has been invoked by the courts. Chief Justice Marshall, in United States v. The Schooner Peggy, 5 U.S. (1 Cranch) 103, 2 L.Ed. 49 (1801), wrote that generally if, while an appeal is pending, the governing rule is changed by an intervening law, then the latter must be applied. The Chief Justice, however, was concerned there with a case involving the national interest and not merely with substantive rights previously, as here, established by private parties. In Bradley v. Richmond School Board, 416 U.S. 696, 94 S.Ct. 2006, 40 L.Ed.2d 476 (1974), the Court noted that the reasoning of Schooner Peggy applies “where the change [is] constitutional, statutory, or judicial.” Id. at 715, 94 S.Ct. at 2018. The rule of Schooner Peggy is further subject, however, to exception when application of the modification would result in manifest injustice, or there is statutory direction or legislative history to the contrary. Id. at 711, 94 S.Ct. at 2016.
We turn to the statute under consideration and find its language equivocal. Congress simply provided that the amendment prohibiting involuntary retirement before age 65 “shall take effect on the date of enactment of this Act [April 6,1978].” This wording is inconclusive. It could mean, as defendant urges, that no such retirements could take place after April 6,1978. On the other hand, plaintiffs argue that the amendment erased conflicting provisions from existing retirement plans and eliminated defenses based on contractual language. Because both interpretations of the statutory language are plausible, we examine the legislative history.
Congressional efforts to revise § 4(f)(2) of the ADEA, 29 U.S.C. § 623(f)(2) (1976), began in 1977 after the Court of Appeals for the Fifth Circuit in Brennan v. Taft Broadcasting Co., 500 F.2d 212 (5th Cir. 1974), and this court in Zinger v. Blanchette, supra, concluded that the Act permitted involuntary retirements before age 65 under a bona fide employee benefit plan. Legislation was introduced in both the House and Senate to amend § 4(f)(2) by providing that employee benefit plans that permitted or required forced, early retirement solely because of age would not be exempt from the Act’s coverage. In addition, the bills proposed raising the upper age limit of the Act incrementally to 70, as in S. 1784,5 or without limit, as in S. 1583.6 As amended and reported from the House Committee on Education and Labor, a third bill, H.R. 5383,7 extended coverage to age 70 after a waiting period of six months.
A study of the House and Senate floor debate reveals only one clear reference to the question of retroactivity. On October 19, 1977, the Senate passed an amended version of H.R. 5383. Most of the floor discussion centered on the exemption of certain occupations from a prohibition against involuntary retirement between ages 65 and 70. At the close of the debate, however, and after the Senate had voted to approve the measure, Senator Jennings Randolph posed the following question:
“Mr. Randolph: I should like to ask the Senator from New Jersey (Mr. Williams) whether this bill retroactively covers a forced retirement at, say, age 60 or 62 prior to the effective date of this bill where the individual so retired is eligible for, and actually receives, a pension under a pension plan which has been qualified with the Internal Revenue Service?
Mr. Williams: The bill is not retroactive. The question of mandatory retirements prior to the effective date of this bill will be determined by the courts’ interpretation of existing law.”
123 Cong.Rec. S 17304 (daily ed. Oct. 19, 1977).8 The bill then went to a conference *1121committee whose members included both Senators Williams and Randolph. But in the interim, the Supreme Court reversed the court of appeals’ decision in McMann v. United Air Lines, Inc., 542 F.2d 217 (4th Cir. 1976), and agreed with the conclusions in Brennan v. Taft Broadcasting Co., supra, and Zinger v. Blanchette, supra, that § 4(f)(2) as originally enacted did not ban pension plan provisions calling for involuntary retirement before age 65. Nevertheless, the conference committee did not change the effective date of the amended § 4(f)(2) to have it apply to former employees who had been retired before they reached the age of 65.
Recognizing, however, that many existing collective bargaining agreements permitted retirement of persons over 65 and under 70 at the option of the employer, the conference committee adopted a Senate provision delaying the impact of the amended § 4(f)(2) on those plans until the expiration date of the agreement or January 1, 1980, whichever occurred first. The net effect, therefore, was to delay the implementation of the substantive amendments except the one pertaining to forced retirements before age 65, which took effect upon enactment.
Further congressional commentary, after the Supreme Court’s reversal in McMann, provides indirect support for the view that the amendment was not intended to apply retrospectively. During the Senate debate on the conference report, in commenting on the amendment to § 4(f)(2), Senator Williams, the floor manager, stated:
“The conference agreement also clarifies existing law to insure that pension plans or seniority systems which require mandatory retirement may no longer be applied to employees covered by the act.”
124 Cong.Rec. S 4449 (daily ed. March 23, 1978) (emphasis supplied). On the House floor, Representative Hawkins, the floor manager, noted that the Supreme Court’s interpretation of the 1967 Act in McMann allowed retirement under that plan and said, “By virtue of this amendment [to § 4(f)(2)], such a plan no longer falls within the § 4(f)(2) exception.” 124 Cong.Rec.H 2270 (daily ed. March 21, 1978) (emphasis supplied). These remarks, though not as explicit as the earlier discussion between Senators Williams and Randolph, are nevertheless consistent with it. To the extent that it is relevant, therefore, the legislative history tends to support the conclusion that Congress did not intend that the amendment retroactively benefit those who had been retired before the effective date of the legislation.
The repeated references in the legislative history to Congress’s intent to “clarify” the meaning of § 4(f)(2) do not justify an inference that the amendment was to be retroactive. Nor does the fact that Congress specifically disagreed with the Supreme Court’s interpretation of § 4(f)(2) in McMann necessitate the conclusion that Congress meant to legislate retrospectively. As we held in United States v. Richardson, 512 F.2d 105 (3d Cir. 1975), references in the legislative history demonstrating a congressional desire to overcome a specific Supreme Court decision do not determine whether Congress also intended to affect events that had occurred before the enactment date.
The district courts confronted with the issue of the applicability of the amendments to § 4(f)(2) have with but one exception concluded that it should be read prospectively. Marshall v. Delaware River & Bay Authority, 471 F.Supp. 886 (D.Del.1979); Marshall v. Atlantic Container Line, 470 F.Supp. 71 (S.D.N.Y.1978); Marshall v. Bal*1122timore & Ohio Railroad Co., 461 F.Supp. 362 (D.Md.1978), appeal docketed, Nos. 79-1210-1211 (4th Cir. March 29,1979); Aldendifer v. Continental Air Lines, 18 Empl. Prac.Dec. 18874 (C.D.Cal.1978), appeal docketed, No. 79-3104 (9th Cir. Jan. 25, 1979). Contra, Davis v. Boy Scouts, 457 F.Supp. 665 (D.N.J.1978); cf. Marshall v. American Motors Corp., 475 F.Supp. 875, (E.D.Mich.1979) (citing Davis v. Boy Scouts, supra, with approval but not reaching the issue of application to pending cases). Thus, the statutory language is not determinative and the brief legislative history ?eems to indicate that Congress intended a respective application.
We must also consider the final exception to the Bradley presumption of retroactivity, classified broadly as one where applying the statute “would result in manifest injustice.” 416 U.S. at 711, 94 S.Ct. at 2016. As the Court stated, “[Neither our decision in Thorpe [v. Housing Authority, 393 U.S. 268, 89 S.Ct. 518, 21 L.Ed.2d 474 (1969)] nor our decision today purports to hold that courts must always thus apply new laws to pending cases in the absence of clear legislative direction to the contrary . . . .” 416 U.S. at 715, 94 S.Ct. at 2018. Although the precise category of cases to which the “manifest injustice” exception applies has not been clearly defined, the Bradley opinion commented that “the Court in Schooner Peggy suggested that such injustice could result ‘in mere private cases between individuals,’ and implored the courts to ‘struggle hard against a construction which will, by a retrospective operation, affect the rights of parties.’ ” Id. at 717, 94 S.Ct. at 2019, quoting United States v. The Schooner Peggy, supra at 110.9 In this context, the Bradley Court suggested analysis of “(a) the nature and identity of the parties, (b) the nature of their rights, and (c) the nature of the impact of the change in law upon those rights.” Id. at 717, 94 S.Ct. at 2019.
In Bradley, the defendant was a school board, a public body supported by taxation, and the plaintiffs were individuals aggrieved by unconstitutional actions of that body. In contrast, the matter at bar is a private case between nonpublic entities. The plaintiffs seek reinstatement and damages for what they assert were premature retirements. Moreover, unlike the situation in Schooner Peggy, which involved national treaty interpretation, resolution of this case would not cause repercussions in the international community, nor would it implicate long standing constitutional violations as in Bradley. Indeed, that Court pointed out that “school desegregation litigation is of a kind different from ‘mere private cases between individuals.’ ” Id. at 718, 94 S.Ct. at 2019.10
We must also consider the nature of the parties' substantive rights and the impact that application of the 1978 amendment would have on those contractual rights and obligations. Both plaintiffs voluntarily elected to- join defendant’s retirement plan, thus forming a contract that was prima facie in compliance with the law when the retirements occurred. For at that time, an interpretive bulletin, 29 C.F.R. § 860.110 (1979), issued by the Secretary of Labor in 1969 was in effect and stated: “Thus, the act authorizes involuntary retirement irrespective of age, provided that such retirement is pursuant to the terms of a retirement or pension plan meeting the requirements of § 4(f)(2).” In January 1975, the then Secretary of Labor, without changing the interpretive bulletin, took the position that retirements before 65 were not permis*1123sible unless they were required by the terms of the plan and were essential to the plan’s economic survival or to some other legitimate purpose.11 That position, however, has not survived judicial scrutiny as evidenced by the decisions in Taft Broadcasting and Zinger.
Indeed, the Taft Broadcasting decision, filed in 1974, was the only appellate decision that had been handed down at the time the plaintiffs were retired. Thus, at that time the defendant had an interpretive ruling of the Secretary of Labor and a court of appeals’ opinion sustaining the position that the ADEA permitted involuntary retirement before age 65.12 Plaintiffs at that juncture therefore had no firmly established right to continue in employment until they reached the age of 65. On the other hand, much as we sympathize with plaintiffs’ position, the defendant had the contractual option to retire its employees as permitted by the plan. To that extent, the rights and obligations of the company — and of the plaintiffs as well — had been fixed and in place in 1975 and 1976 when they retired. In such circumstances, post-Bradley cases have declined to apply new law to pending cases. See National Consumer Information Center v. Gallegos, 549 F.2d 822, 826-27 (D.C.Cir.1977). See also Greene v. United States, 376 U.S. 149, 84 S.Ct. 615, 11 L.Ed.2d 576 (1964); Claridge Apartments Co. v. Commissioner, 323 U.S. 141, 65 S.Ct. 172, 89 L.Ed. 139 (1944); Hospital Employees Labor Program v. Ridgeway, 570 F.2d 167 (7th Cir. 1978); Weise v. Syracuse University, 522 F.2d 397 (2d Cir. 1975).
Nor can we overlook the fact that rulings that may conceivably upset the solvency of pension plans have been given special consideration by the Supreme Court. In Los Angeles Department of Water & Power v. Manhart, 435 U.S. 702, 98 S.Ct. 1370, 55 L.Ed.2d 657 (1978), the Court concluded that it was improper to award retroactive relief in a Title VII case where sex differentiated employee contributions to a pension fund were found to be impermissible. Noting that “[djrastic changes in the legal rules governing pension and insurance funds” can jeopardize their solvency the Court said, “Consequently, the rules that apply to these funds should not be applied retroactively unless the legislature has plainly commanded that result.” Id. at 721, 98 S.Ct. at 1382.13 Although this statement appears in a different context than that present here, nevertheless it appears particularly pertinent in view of the Bradley admonition to consider the nature of the rights being litigated and the nature of the impact of the change in law upon those rights.
The presumption in favor of retroactivity articulated in Bradley, therefore, is inapplicable to the case sub judice because of the positive legislative history and the “need to prevent manifest injustice.” Accordingly, we conclude that the 1978 amendments *1124must not be applied to retirements that occurred before the effective date of the legislation.
Plaintiffs also contend that our decision in Zinger v. Blanchette, supra, misinterpreted the ADEA and we should now adopt the position taken by Congress in enacting the amendments. The Supreme Court, however, confronted the same argument in McMann and rejected it, saying, “Legislative observations 10 years after passage of the Act are in no sense part of the legislative history.” 434 U.S. at 200 n. 7, 98 S.Ct. at 449. Moreover, even if we were inclined to do so, this panel is not free to reconsider Zinger. United States Court of Appeals for the Third Circuit Internal Operating Procedure VIII-C.
In the district court, plaintiffs alleged that the American Can retirement plan was both a subterfuge and not bona fide. Although they did not brief the matter on appeal, we do have the benefit of the research on the point in the Secretary’s brief. Since this case must be returned to the district court in any event, we consider the issue for the guidance of the district court. It is argued that the plan is not bona fide within the meaning of Rogers v. Exxon Research & Engineering Co., 550 F.2d 834, 838 (3d Cir. 1977), cert. denied, 434 U.S. 1022, 98 S.Ct. 749, 54 L.Ed.2d 770 (1978), and Zinger v. Blanchette, supra at 905, 909 & n.20; accord, Marshall v. Hawaiian Telephone Co., 575 F.2d 763, 766 (9th Cir. 1978), because the earliest age at which retirement is permitted is too low and the pensions are inadequate. The district court said that the plan was bona fide but the record does not reveal the factual basis for that conclusion, which has been disputed by the plaintiffs. Therefore, we are not in a position to pass upon plaintiffs’ contentions that the age limit for early retirement is too low and the pensions are inadequate.
Moreover, the contention that the plan was a subterfuge cannot be resolved on this record. The Supreme Court held in McMann that a plan established before passage of the Act in 1967 was not a subterfuge. Alterations made to a plan after ADEA was in effect, however, may be examined to see if the changes were designed to evade the purposes of the Act. A copy of the 1974 plan is part of the record but whether that includes significant changes from the 1959 plan is not apparent to us. Since the case must be returned to the district court for a resolution of the claims of discrimination in denying raises, the court on remand should also permit the plaintiffs to develop their contentions that the plan is not bona fide and is, in fact, a subterfuge.
The judgment of the district court will be vacated and remanded for further proceedings consistent with this opinion. The parties shall bear their own costs.
. A third plaintiff, John Sikora, retired at age 59 on a monthly pension of $767.46, reduced to $564.00 on January 1, 1979 and payable thereafter for life. He had worked for the company since 1930 except for a period of four years. He joined the plan in 1964. At time of retirement, his salary was $1,199.00 per month. Sikora settled his case after this appeal was taken. The claim of Frederick Meyer, the fourth plaintiff was dismissed by stipulation.
. As enacted in 1967, 29 U.S.C. § 623 (1976) read in pertinent part:
“(f) It shall not be unlawful for an employer, employment agency, or labor organization—
******
(2) to observe the terms of a bona fide seniority system or any bona fide employee benefit plan such as a retirement, pension, or insurance plan, which is not a subterfuge to evade the purposes of this chapter, except ‘ that no such employee benefit plan shall excuse the failure to hire any individual.”
. The first appeal taken by the plaintiffs was dismissed by this court because of a lack of compliance with Fed.R.Civ.P. 54(b). The district court thereafter entered an appropriate order and consequently we now have jurisdiction to consider this appeal.
. As amended in 1978, 29 U.S.C. § 623 (Supp. II 1978) reads in relevant part:
“(f) It shall not be unlawful for an employer, employment agency, or labor organization—
******
(2) to observe the terms of a bona fide seniority system or any bona fide employee benefit plan such as a retirement, pension, or insurance plan, which is not a subterfuge to evade the purposes of this chapter, except that no such employee benefit plan shall excuse the failure to hire any individual, and no such seniority system or employee benefit plan shall require or permit the involuntary retirement of any individual specified by section 631(a) of this title because of the age of such individual.”
. S. 1784, 95th Cong., 1st Sess., 123 Cong.Rec.S 11108 (daily ed. June 29, 1977).
. S. 1583, 95th Cong., 1st Sess., 123 Cong.Rec. 16101-02 (1977).
. H.R. 5383, 95th Cong., 1st Sess. (1977).
. Both Senators Williams and Randolph were members of the Senate Human Resources Committee, which had brought the bill to the floor. The exchange between the two Senators was obviously intended to create a “legislative history.” The reference to the “courts’ interpretation of existing law” must be understood *1121in light of the fact that the McMann case had been argued before the Supreme Court two weeks earlier. The congressional committees considering the ADEA amendments had previously expressed their approval of the opinion of the court of appeals in McMann v. United Air Lines, Inc., 542 F.2d 217 (4th Cir. 1976), which held that the ADEA prohibited mandatory retirement based on age before 65. E.g., S.Rep. No. 493, 95th Cong., 1st Sess. 10, reprinted in [1978] U.S.Code Cong. & Admin.News, pp. 504, 513.
. Schooner Peggy presented a matter of national policy, a critical distinction from the case at bench. In announcing the rule, Chief Justice Marshall cautioned against an application of statutory construction even as to a pending case when it affects the rights of private parties.
. In United States v. Alabama, 362 U.S. 602, 80 S.Ct. 924, 4 L.Ed.2d 982 (1960), the Court applied recently enacted legislation to permit suits directly against states for violations of voting rights. The legislative history reflects Congress’s knowledge that the statute was intended to apply to the case then pending before the Supreme Court. See 106 Cong.Rec. 7605, 7615 (1960). Moreover, the suit sought enforcement of preexisting rights.
. In a report to Congress, Secretary Brennan stated:
“[R]etirements [before 65] are unlawful unless the mandatory retirement provision: (1) is contained in a bona fide pension or retirement plan, (2) is required by the terms of the plan and is not optional, and (3) is essential to the plan’s economic survival or to some other legitimate purpose— i. e., is not the plan for the sole urpose [sic] of moving out older workers, which purpose has not been made unlawful by the ADEA.”
Dept, of Labor, January 1975 report pertaining to activities in connection with the Age Discrimination in Employment Act of 1967, at 17 (1975) .
. Section 7(e) of ADEA, 29 U.S.C. § 626(e) (1976) , incorporates the good faith defense set out in the Portal To Portal Act:
“[N]o employer shall be subject to any liability . . if he pleads and proves that the act or omission complained of was in good faith in conformity with and in reliance on any written administrative regulation, order, ruling, approval, or interpretation of the agency.” 29 U.S.C. § 259 (1976).
. Turning aside the plaintiffs’ contention that the award in that case would not be crippling to the defendants because it was limited to contributions for three years, the Court stated, “[W]e cannot base a ruling on the facts of this case alone.” Los Angeles Dept. of Water & Power v. Manhart, supra at 722 n.42, 98 S.Ct. at 1382. Nor can we look only to the number of claims pending against American Can.