Justices of the U.S. Supreme Court, including conservative ones, have raised questions about the legality of the Donald Trump administration’s imposition of sweeping tariffs.

They argued over whether Mr Trump has the authority to impose sweeping tariffs under a 1977 emergency law.

The judges heard arguments from the administration and opponents of Mr Trump’s actions in a session lasting more than two hours on Wednesday.

It was unclear when a ruling would be handed down, but U.S. media reported it could take weeks to months.

Justice John Roberts, an appointee of Republican President George W. Bush, said during the hearing that “the vehicle is an imposition of taxes on Americans, and that has always been the core power of Congress”.

The case concerns country-specific tariffs first announced by Mr Trump in April, targeting dozens of U.S. trading partners, for which the administration later adjusted some rates.

In invoking the International Emergency Economic Powers Act of 1977, Mr Trump argued that trade deficits with other nations posed a national security risk, justifying tariffs without congressional approval.

However, an appeals court disagreed, saying tariffs fell within Congress’s remit and dealt a blow to Trump’s aggressive trade policy.

In its appeal, the Trump administration argued that stripping the president of this tariff authority would endanger trade deals struck with major partners, arguing that the agreements were negotiated under pressure from the contested tariffs.

Justices Amy Coney Barrett and Neil Gorsuch, both Mr Trump appointees, were particularly critical of the administration’s arguments and questioned why almost all U.S. trading partners were classified as threats to national security.

Mr Barrett said, “I want to ask you about an unusual threat that we haven’t talked about yet: the reciprocal tariffs. Is it your contention that every country needed to be tariffed because of threats to the defence and industrial base? I mean, Spain, France.”

“I could see it with some countries, but explain to me why many countries needed to be subjected to the reciprocal tariff policy,” she told the U.S. solicitor-general, D. John Sauer, who was arguing for the Trump administration,

Mr Gorsuch, who warned against a unilateral shift of power in favour of the president and at the expense of Congress, said, “This, according to the Constitution, is the government branch with the power to levy taxes and customs duties.”

(dpa/NAN)