The U.S. Supreme Court ruled Friday that judges should not defer to expert federal agencies during legal fights over regulations, overturning 40 years of “Chevron deference” in a massive blow to the administrative state.

Chief Justice John Roberts Jr. read from the bench the court’s 6-3 decision to overturn the legal doctrine, saying it sprang from the court’s “fundamentally misguided decision” in the 1984 case Chevron USA v. Natural Resources Defense Council.