Pursuant to § 10(j) of the Endangered Species Act (ESA), the U.S. Fish and Wildlife Service (FWS) captured a population of endangered red wolves located in North Carolina and Tennessee, bred them in captivity, and then reintroduced them into the wild on federally-protected refuges. As part of that effort, the FWS enacted 50 C.F.R. § 17.84(c), a regulation that prevented private landowners from harassing, injuring, or killing the wolves if they escaped from the refuges. Approximately 40 of the 75 wolves wandered off the refuges and onto private lands. Charles Gibbs, other North Carolina residents and counties (plaintiffs), filed suit in federal court against Bruce Babbitt, in his official capacity as Secretary of the Interior, the FWS and others (defendants) challenging the constitutionality of § 17.84(c) and arguing that Congress lacked the authority under the Commerce Clause to protect the wolves found on private land. The district court, on cross-motions for summary judgment, held for defendants and concluded that Congress’ power to regulate interstate commerce extended to regulating the endangered, protected wolves found on private land. Plaintiffs appealed.