U.S. Supreme Court justices expressed scepticism on Wednesday about the legality of President Donald Trump’s wide-ranging tariffs, in a landmark case that could have major consequences for the global economy and test the limits of presidential power.

Both conservative and liberal justices sharply questioned the Trump administration’s lawyer over whether a 1977 law — intended for use during national emergencies — actually granted Trump the authority to impose such tariffs, or whether he had encroached on Congress’s constitutional powers.

However, several conservative justices emphasised the president’s traditional authority in foreign affairs, signalling the possibility of a divided ruling. The court currently holds a 6–3 conservative majority.

The hearing, which lasted more than two and a half hours, concerned appeals by the administration after lower courts ruled that Trump had exceeded his powers in using the law to justify the tariffs. The measures were challenged by affected businesses and 12 U.S. states, mostly led by Democrats.

Debate over presidential authority

Chief Justice John Roberts told U.S. Solicitor General D. John Sauer that the tariffs represented “the imposition of taxes on Americans — and that has always been the core power of Congress.”

Tariffs, effectively taxes on imports, could raise trillions of dollars for the U.S. over the next decade, but the Constitution assigns Congress the power to levy taxes and duties.

Roberts suggested that the court’s “major questions” doctrine might apply — requiring clear congressional authorisation for executive actions with vast economic or political implications.

“The justification is being used to grant power to impose tariffs on any product, from any country, in any amount, for any length of time,” Roberts said. “That’s a major authority, and the basis for that claim seems questionable.”

The same doctrine has previously been used to strike down significant policies introduced by Trump’s Democratic predecessor, Joe Biden.

Trump has urged the Supreme Court to uphold the tariffs, a central pillar of his economic and foreign policy strategy. A ruling against him would mark a notable shift from earlier cases in which the court supported some of his most far-reaching actions — from immigration restrictions to the dismissal of federal officials and bans on transgender military personnel.

The IEEPA and its limits

Trump invoked the International Emergency Economic Powers Act (IEEPA) to justify tariffs on nearly all U.S. trading partners. The law allows a president to regulate commerce in times of national emergency, but Trump is the first to use it for tariffs — another instance of his administration testing executive boundaries since his return to office in January.

Conservative Justice Amy Coney Barrett questioned whether the IEEPA’s language about regulating “importation” could be stretched to mean imposing tariffs.

“Can you point to any other instance where that phrase has been used to confer tariff authority?” she asked.

Liberal Justice Ketanji Brown Jackson argued the law was designed to restrict presidential power, not expand it.

“It’s quite clear Congress intended to constrain, not enlarge, the president’s emergency powers,” she said.

While the Supreme Court typically takes months to issue rulings, the administration has asked for a swift decision.

Treasury Secretary Scott Bessent, who attended the hearing, later told Fox Business he was “very, very optimistic,” and said the administration would rely on alternative legal mechanisms if it lost the case.

A global trade flashpoint

The IEEPA was originally designed to allow the president to address “unusual and extraordinary threats” in a national emergency, historically used to impose sanctions or freeze assets.

Sauer argued that Trump deemed America’s trade deficits an economic and national security emergency, and that tariffs had been instrumental in negotiating trade deals. Dismantling them, he warned, would expose the U.S. to “ruthless trade retaliation” and “ruinous economic and security consequences.”

Trump’s use of tariffs has already fuelled a global trade war, straining relations with major partners, unsettling financial markets, and stoking uncertainty. He has wielded tariffs not only to reshape trade agreements but also to pressure countries on unrelated political issues — for example, citing them as leverage against China, Canada, and Mexico to curb fentanyl trafficking.

Divisions on the bench

Sauer argued that the “major questions” doctrine should not apply in matters of foreign policy. Conservative Justice Brett Kavanaugh appeared sympathetic, pointing out that President Richard Nixon had imposed global tariffs under a similar statute in the 1970s.

“That’s a good precedent for you,” Kavanaugh remarked.

The court has traditionally deferred to presidents on foreign affairs, and Roberts acknowledged that Trump’s tariffs had given him “leverage in trade negotiations.”

Between February and September, the IEEPA-based tariffs generated roughly $89 billion in revenue, according to U.S. Customs data.

“Yes, tariffs are a tax, and that’s Congress’s domain,” Roberts said, “but they are also a foreign-facing tax — and foreign policy is core to the executive branch.”

Yet Justice Neil Gorsuch warned that embracing such an expansive view of presidential authority could erode the Constitution’s separation of powers.

“What would stop Congress from abdicating all responsibility for regulating foreign commerce — or even declaring war — to the president?” he asked.

A ruling in the case could redefine the balance of power between Congress and the presidency — and determine how far Trump can go in using emergency powers to reshape global trade.

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