Trump’s administration is trying to defend his tariffs after lower courts ruled that he had exceeded his authority in using a 1977 federal law to impose tariffs.

The lawyer representing United States President Donald Trump’s administration is facing tough questions from conservative and liberal US Supreme Court justices over the legality of the Republican president’s sweeping tariffs in a case with implications for the global economy that marks a major test of Trump’s powers.

On Wednesday, the justices pressed US Solicitor General D John Sauer, arguing for the administration, about whether Trump had intruded on the power of Congress in imposing tariffs under a 1977 law meant for national emergencies. They also asked Sauer whether Trump’s application of the statute to impose tariffs of unlimited duration was a major action by the executive branch that would require clear congressional authorisation.

The arguments come in appeals pursued by the administration after lower courts ruled that his unprecedented use of a 1977 federal law at issue to impose the tariffs exceeded his authority. Businesses affected by the tariffs and 12 US states, most of them Democratic-led, challenged the tariffs.

Trump has heaped pressure on the Supreme Court, which has a 6-3 conservative majority, to preserve tariffs that he has leveraged as a key economic and foreign policy tool.