The US Supreme Court on Wednesday expressed scepticism over President Donald Trump’s sweeping global tariffs imposed under the International Emergency Economic Powers Act (IEEPA) of 1977, in a pivotal case that could reshape the limits of presidential authority over trade.

The nine justices deliberated on whether Trump lawfully used the emergency powers law to levy tariffs on imports from more than 100 countries — measures that have disrupted global trade, increased costs for US consumers, and triggered retaliation from trading partners.

The lawsuits, filed by 12 US states led by Oregon and several small businesses, argue that the IEEPA does not empower a President to impose tariffs unilaterally. They maintain that the power to tax imports rests exclusively with Congress, as defined by the US Constitution’s separation of powers.

Representing the petitioners, Indian-American lawyer Neal Katyal contended that Congress “never gave the President authority to overhaul the entire tariff system and the American economy,” emphasizing that IEEPA was never intended to grant such sweeping powers.

Chief Justice John Roberts questioned the administration’s interpretation of the law, remarking that tariffs function as “taxes on Americans,” a traditional domain of Congress. Justice Brett Kavanaugh cited Trump’s 50 per cent tariffs on India, calling it “unusual” to classify such trade actions as emergencies.

Defending the policy, US Solicitor General John Sauer argued that the tariffs were a lawful exercise of executive power to “regulate foreign commerce,” and that any revenue raised was incidental. He warned that removing this authority could weaken America’s leverage in future trade negotiations.

Lower courts, including the US Court of Appeals for the Federal Circuit, have already ruled against Trump’s use of IEEPA, finding his tariffs exceeded presidential authority. Earlier, the International Trade Court struck down his Liberation Day and fentanyl-related tariffs on China and Canada.

More than 40 amicus briefs have been filed, including one from 207 lawmakers — among them only one Republican, Senator Lisa Murkowski — who pointed out that “neither the word ‘duties’ nor ‘tariffs’ appears anywhere in the IEEPA.”

If the Supreme Court rules against the administration, it could trigger refunds exceeding $100 billion in collected duties since 2022, with major implications for global trade and executive power. A decision is expected in early 2026.