In the case of Puerto Rico Department of Consumer Affairs v. Isla Petroleum Corporation, 1987, the U.S. Supreme Court ruled that a Puerto Rican law which regulated oil prices was not preempted by federal antitrust laws and thus could be enforced. The court held that while Congress had intended to deregulate petroleum pricing at the federal level, it did not intend to prevent states from implementing their own regulations on petroleum pricing. Therefore, Puerto Rico's price control law was valid and enforceable despite being more restrictive than federal regulations.

In the dissenting opinion for Puerto Rico Department of Consumer Affairs v. Isla Petroleum Corporation, Justice Scalia disagreed with the majority's interpretation of Section 5(b) of the Emergency Petroleum Allocation Act (EPAA). He argued that this section does not grant states or territories like Puerto Rico any authority to regulate prices in a manner inconsistent with federal regulations. According to him, Congress intended for EPAA to create uniform national pricing standards and did not intend for individual states or territories to deviate from these standards. Therefore, he believed that Puerto Rico's attempt at price regulation was preempted by federal law under EPAA. Furthermore, he criticized the majority’s reliance on legislative history rather than clear statutory text as an interpretive method.