The U.S. Supreme Court has begun hearings to determine the legality of global tariffs imposed by President Donald Trump on countries including South Korea.

The court heard arguments in the case Wednesday at its courthouse in Washington, D.C. 

The key question in the nearly three-hour hearing was whether Trump’s invocation of the 1977 International Emergency Economic Powers Act provided a legal basis for the tariffs.

Solicitor General John Sauer, representing the U.S. government, told the justices that Trump invoked emergency powers because he believed the trade deficit had pushed the United States to the brink of an economic and national security crisis.

Neal Katyal, the attorney representing small businesses challenging the tariffs, countered that “a tariff is a tax,” emphasizing that the Constitution gives the power to tax solely to Congress.

Lower courts, including a specialized trade court, a district court in Washington and a federal appeals court, ruled in favor of the challengers, finding that Trump lacked the legal authority to impose the tariffs under the emergency powers law.