(AP) — The U.S. Supreme Court heard arguments Wednesday over President Donald Trump’s sweeping tariffs, putting a tool at the center of his economic and foreign policy agendas squarely before the high court.

The case involves the tariffs first announced in April on almost all U.S. trading partners and the ones from February on imports from Canada, China and Mexico. Trump justified these by declaring separate national emergencies under the International Emergency Economic Powers Act, or IEEPA.

Earlier this year, however, two lower courts and a federal appeals court ruled that the emergency law he invoked doesn’t give him unlimited power to set tariffs. The Constitution says tariff power belongs to Congress.

Now, arguments on whether the president’s tariffs overstep federal law arrive before a conservative-led Supreme Court, which has thus far been reluctant to check Trump’s wide-ranging use of executive powers.

It was a “hot bench,” with every justice posing multiple questions on an issue of extreme importance. But when the court will issue its decision is unclear. High-profile cases can take half a year, but the court can act quickly when deadline pressure dictates.