The Federal Energy Regulatory Commission (FERC) (defendant) voted to include reopener clauses in existing licenses for water-power projects, in order to require licensees to construct fishway facilities that protected migrating fish. FERC included the clauses under the authority of § 18 of the Federal Power Act (FPA), 16 U.S.C. § 811. The reopener clauses allowed FERC to require fishways upon its own motion or the recommendations of other agencies. The Wisconsin Public Service Corporation (WPS) (plaintiff) appealed the inclusion of the reopener clauses to FERC, which rejected the appeal. WPS petitioned for review, objecting to the ability of other agencies to impose requirements without balancing project costs, and to the inability of licensees to determine costs in advance. Specifically, WPS claimed that State of California v. FPC, 345 F.2d 917 (9th Cir. 1965), which upheld a reopener clause, was inapplicable for a variety of reasons, including addressing FERC’s authority rather than the authority of other agencies, concerning foreseeable circumstances, and taking project economics into account. Regarding reasonableness, WPS argued that FERC’s interpretation of § 18 conflicted with § 15 of the FPA, which required new licenses to be issued to original licensees on reasonable terms. WPS also claimed that FERC’s interpretation of § 18 violated the Administrative Procedure Act (APA), because there was no evidence that fishways would be required for WPS’s projects in the future.