President Donald Trump raised the global duty on imports into the United States to 15 per cent on Saturday (Feb 21), doubling down on his promise to maintain his aggressive tariff a day after the US Supreme Court ruled much of it illegal.

Trump said on his Truth Social platform that after a thorough review of Friday's "extraordinarily anti-American decision" by the court to rein in his tariff programme, the administration was hiking the import levies "to the fully allowed, and legally tested, 15 per cent level."

Shortly after the court's 6-3 ruling that rejected the president's authority to impose tariffs under a 1977 economic emergency powers act, Trump had initially announced a new 10 per cent global levy by invoking a different legal avenue.

At the same time, the Republicans launched an extraordinary personal attack on the conservative justices who had sided with the majority, slamming their "disloyalty" and calling them "fools and lap dogs".

The ruling was a stunning rebuke by the high court, which has largely sided with the president since he returned to office, and marked a major political setback in striking down Trump's signature economic policy that has roiled the global trade order.

Saturday's announcement is sure to provoke further uncertainty as Trump carries on with a trade war that he has used to cajole and punish countries, both friend and foe.

It is the latest move in a process that has seen a multitude of tariff levels for countries sending goods into the United States set and then altered or revoked by Trump's team over the past year.

The new duty by law is only temporary - allowable for 150 days. According to a White House fact sheet, exemptions remain for sectors that are under separate probes, including pharma, and goods entering the US under the US-Mexico-Canada agreement.

On Friday, the White House said US trading partners that reached separate tariff deals with Trump's administration would also face the new global tariff.