opinion: CITY OF PHILADELPHIA et al. v. NEW JERSEY et al.
  No. 75-1150.
  Argued November 3, 1976
  Decided February 23, 1977
  Herbert F. Moore argued the cause for appellants. With him on the briefs were Arthur Meisel and John R. Padova.
  Stephen Skillman, Assistant Attorney General of New Jersey, argued the cause for appellees. With him on the brief were William F. Hyland, Attorney General, and Mark L. First, Deputy Attorney General.
  M. Jerome Diamond, Attorney General of Vermont, Benson D. Scotch, Assistant Attorney General, David H. Souter, Attorney General of New Hampshire, and Donald W. Stever, Jr., Assistant Attorney General, filed a brief for the States of Vermont and New Hampshire as amici curiae urging affirmance.
  Briefs of amici curiae were filed by Louis L. Meier, Jr., for the American Society of Civil Engineers, and by William C. Brashares for the National Solid Wastes Management Assn.
  Per Curiam.
  This suit challenges the constitutionality of a New Jersey statute prohibiting any person from bringing into New Jersey “any solid or liquid waste which originated or was collected outside the territorial limits of the State," except garbage to be fed to swine. 1973 N. J. Laws, c. 363. The New Jersey Supreme Court held that the Act was not pre-empted by a federal statute addressing questions of waste disposal, the Solid Waste Disposal Act of 1965, 79 Stat. 997, 42 U. S. C. § 3251 et seq. (1970 ed. and Supp. V), and was not unconstitutional as discriminating against or placing an undue burden on interstate commerce. Hackensack Meadowlands Dev. Comm’n v. Municipal Sanitary Landfill Authority, 68 N. J. 451, 348 A. 2d 505 (1975). We noted probable jurisdiction on April 5, 1976, 425 U. S. 910.
  On October 21, 1976, the Resource Conservation and Recovery Act of 1976, 90 Stat. 2795, 42 U. S. C. § 6901 et seq. (1976 ed.), became law. The parties at the Court’s request supplemented their briefs to address the question of the impact of the new federal statute on the New Jersey Act. Appellants argue that the Federal Act displaces the New Jersey law, and appellees argue that it does not preempt or in any way undercut the validity of the New Jersey legislation. While federal pre-emption of state statutes is, of course, ultimately a question under the Supremacy Clause, U. S. Const., Art. VI, cl. 2, analysis of pre-emption issues depends primarily on statutory and not constitutional interpretation. Therefore, it is appropriate that the federal preemption issue be resolved before the constitutional issue of alleged discrimination against or undue burden on interstate commerce is addressed. We think it appropriate that we have the views of the New Jersey Supreme Court on the question whether or to what extent the Resource Conservation and Recovery Act of 1976 pre-empts the New Jersey statute. The judgment of the New Jersey Supreme Court is therefore vacated, and the case is remanded for reconsideration in light of that Act.
  So ordered.
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