The U.S. Supreme court on Friday undid decades of regulatory law, making it far more difficult for federal agencies to issue rules and regulations that carry out broad mandates enacted by Congress. Along ideological lines, the court reversed a 40-year-old precedent that has governed what agencies can and cannot do in interpreting federal statutes.

The decision overturned Chevron v. The Natural Resources Defense Council, a 1984 decision that was not particularly controversial when it was announced 40 years ago. Indeed, the vote was unanimous in declaring that when a statute is ambiguous, courts should defer to reasonable agency interpretations of what it means.