Multinational retail giant Costco has sued the US government to secure a full refund of import duties if the Supreme Court rejects President Donald Trump's authority to impose tariffs without congressional approval.

Costco's lawsuit urges the federal trade court to declare Trump's 'emergency' tariffs illegal, an authority the president says he has under the International Emergency Economic Powers Act (IEEPA).

Two lower courts have already ruled that Trump exceeded his authority by using emergency powers to impose tariffs.

The case has now reached the Supreme Court, and several companies are trying to protect their rights to refunds should the justices strike down the tariffs.

In the lawsuit filed over the Thanksgiving holiday, Costco said its business had suffered because of the tariffs and was concerned it wouldn't get its money back even if the apex court upheld previous rulings.

Lawyers for Costco said a "separate action is necessary" as a refund is not guaranteed "in the absence of their own judgment and judicial relief".

The world's third-largest retailer didn't say how much it was seeking back but trade data from the US customs agency shows importers like Costco have already paid about $90 billion in IEEPA-related tariffs as of late September.

Costco brought the suit to the US Court of International Trade ahead of a 15 December 2025 deadline after which it would struggle to recoup any funds paid to the government.

In May, that court was the first to rule that Trump's tariffs were unlawful, a decision that has been subsequently affirmed by the US Court of Appeals.

At the hearing last month, Supreme Court judges appeared sceptical of the president's authority to impose the levies without congressional approval.

Trump administration lawyers have argued in court the emergency powers give the president the authority to impose the global tariffs.

The administration has warned an unfavourable ruling will restrict its ability to negotiate with countries and the treasury will lose billions already collected.

"The economic consequences of the failure to uphold President Trump's lawful tariffs are enormous, and this suit highlights that fact," White House spokesperson Kush Desai told CNBC in a statement. "The White House looks forward to the Supreme Court's speedy and proper resolution of this matter," the statement added.

Last month, the president said the US was "taking in Trillions of Dollars" in tariffs and promised "a dividend of at least $2000 a person (not including high-income people!) will be paid to everyone".