Going against the tide of recent decisions that limit federal power, the Supreme Court on Monday unanimously declared that federal law reigns supreme over the states when it comes to regulation of oil tankers.

The justices in U.S. v. Locke struck down four Washington state safety regulations enacted after the Exxon Valdez oil spill in 1989. The regulations injected the state into an area of law “where the federal interest has been manifest since the beginning of our Republic,” Justice Anthony Kennedy wrote for the Court.