President Donald Trump‘s sweeping tariff policy faced its first full hearing in court on Tuesday after a group of small businesses challenged the president’s authority to issue the levies.

The hearing in the U.S. Court of International Trade was the first test of Trump’s claim that a law known as the International Emergency Economic Powers Act gives him the authority to issue the tariffs. Citing the “conditions reflected in large and persistent annual U.S. goods trade deficits,” Trump declared a national emergency last month under the IEEPA and announced 10% blanket tariffs on imports into the U.S., alongside higher “reciprocal” rates for select countries, before pausing the higher rates for 90 days a week after their announcement at the beginning of April.