Supreme Court

The case involved two categories of tariffs. Trump imposed one category on virtually every country in the world, ostensibly to repair trade deficits. He imposed the other set of tariffs on Mexico, Canada and China, saying those countries are responsible for the flow of illegal fentanyl into the U.S.

The court rejected Trump’s argument that a 1977 law, the International Emergency Economic Powers Act, implicitly authorized both groups of tariffs.

“Had Congress intended to convey the distinct and extraordinary power to impose tariffs, it would have done so expressly,” Roberts wrote.

The White House didn’t immediately respond to a request for comment.

Stock indexes rose modestly after the decision, while trade- and tariff-exposed stocks gained. The dollar slipped and Treasury yields edged higher.

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.