with whom The Chief Justice joins, dissenting.
I join Mr. Justice Stewart’s conclusion that the evidence as to what Congress did not do in the federal Welfare and Pension Plans Disclosure Act, 72 Stat. 997, 29 U. S. C. § 301 et seg., is insufficient to override national labor policy barring interference by the States with privately negotiated solutions to problems involving mandatory subjects of collective bargaining.
As in Teamsters v. Oliver, 358 U. S. 283, 297 (1959), “[w]e have not here a case of a collective bargaining agreement in conflict with a local health or safety regulation; the conflict here is between the federally sanctioned agreement and state policy which seeks specifically to adjust relationships in the world of commerce.” The statute in this case removes from the bargaining table certain means of dealing with an inevitable trade-off between somewhat conflicting industrial relations goals — the tension between maintaining competitive standards of present compensation and, at the same time, creating a solvent fund for the security of long-term employees upon retirement. In essence, Minnesota has restricted the available options to the fully funded pension plan that vests upon 10 years of service, whenever an employer ceases to operate a place of employment or pension plan. It also imposes a principle of direct liability that well may discourage employer participation in matters of such vital importance to working men and women.
The retroactivity feature of the Minnesota measure exacerbates the degree of interference with the system of free collective bargaining. Here a statute resulting in the imposition on appellee of substantial financial liability, perhaps as large as $19 million, was enacted and took effect at a time when a *517collective-bargaining agreement embodying different provisions continued in force, by virtue of an arbitration decision, even though the plant in question had closed. Essential features of the negotiated plan, including deferred funding of past-service liability, limited employer liability, and a power of termination, were negated by the legislation. The parties were given no opportunity to consider this expansion of liability in determining how the bargain should be struck. It is not unlikely that the provisions of the pension plan in issue would-have been different if the parties could have predicted this statutory development. This is not, therefore, a case where state law serves as a backdrop to negotiations, while affording the parties considerable freedom to" strike the best possible bargain consistent with state substantive policies. This statute became law in midterm, significantly changing the economic balance reached by the parties at the bargaining table.
In the absence of congressional indication to the contrary, or the type of local health or safety regulation adverted to in Oliver, the States may not alter the terms of existing collective-bargaining agreements on mandatory subjects of bargaining. Congress can be expected to take into' account the impact of retroactive legislation on the bargaining process, and often provides for a delayed effective date in order to minimize any disruption.* But the States, because their *518concerns are distinct from the considerations that animate' a national labor policy, are unlikely to weigh — with perception and understanding — the relevant private and public interests. There is little evidence that Minnesota took more than a parochial view of these considerations when it amended retroactively the bargaining agreement of the parties.
Until Congress expresses its will in clearer fashion than the ambiguous pre-emption disclaimer of the 1958 Disclosure Act, ante, at 505, federal labor policy requires invalidation of the type of statute involved in this case. I would affirm the judgment of the Court of Appeals.
Unlike the Minnesota statute, the federal Employee Retirement Income Security Act of 1974 (ERISA), 29 U. S. C. § 1001 et seq. (1970 ed., Supp. V), provides for a careful phasing in of the statute's requirements in the case of collectively negotiated pension plans. For such plans, ERISA funding requirements will apply only to plan years beginning after termination of the collective-bargaining agreement in effect on January 1, 1974, or plan years beginning after December 31, 1980, whichever is earlier. §§ 1061 (c) (1) and 1086 (c) (1) (1970 ed., Supp. V).
This type of considered congressional response to the special problems of arrangements flowing from collective-bargaining agreements is also found in the Equal Pay Act of 1963, § 4, 77 Stat. 57, amending the Fair Labor Standards Act of 1938, 29 U. S. C. §206 (d). Congress provided that in *518the case of bona fide collective-bargaining agreements in effect at least 30 days prior to the date of enactment of the 1963 measure, the amendments would take effect upon the termination of such collective-bargaining agreement or upon the expiration of two years from the enactment date, whichever occurred first.