In the 1975 case, Examining Board of Engineers, Architects and Surveyors v. Flores de Otero, the U.S. Supreme Court held that Puerto Rico was subject to federal civil rights laws despite its status as a commonwealth rather than a state. The case arose when two engineers sued after being denied licenses by Puerto Rico's examining board because they were not residents of the island. They claimed this violated their constitutional right to equal protection under law. In ruling in favor of the plaintiffs, Justice William Brennan wrote for majority stating that Congress had extended U.S constitution’s protections against discrimination to Puerto Rico through various statutes including Civil Rights Act of 1964 and thus it applied equally there as in any state.

In the dissenting opinion for Examining Board of Engineers, Architects and Surveyors et al. v. Flores de Otero (1975), Justice William Rehnquist argued that Puerto Rico should not be considered a state within the context of 42 U.S.C §1983, which provides recourse for citizens deprived of their rights under color of any statute, ordinance or regulation by anyone acting under color of law in any territory. He contended that Congress did not intend to include Puerto Rico as a "state" when it enacted this legislation because at that time Puerto Rico was still being administered as part of the spoils from Spanish-American War with limited self-governance. Therefore, he believed applying this provision to Puerto Rican officials would be an inappropriate extension beyond its original intent and scope.