The U.S. Constitution gives the power to impose taxes — including tariffs — to Congress. But lawmakers have gradually relinquished power over trade policy to the White House. And Trump has made the most of the power vacuum, raising the average U.S. tariff to more than 18%, highest since 1934, according to the Budget Lab at Yale University.

A federal appeals panel heard arguments from states and businesses that seek to invalidate the president’s tariffs.

“IEEPA nowhere mentions tariffs, duties, imposts, or taxes, and no other President in the statute’s nearly 50-year history has claimed that it authorizes tariffs,” the companies added in a filing with the appeals court.