Retail giant Costco is suing the Trump administration in an early effort to secure tariff refunds in case the Supreme Court rules their implementation was illegal. The company claims the administration is refusing to extend a deadline that effectively makes the tariffs non-refundable in the event it loses at the high court.

President Trump relied on the International Emergency Economic Powers Act to apply tariffs on almost all goods coming into the country during a “Liberation Day” announcement in April.

Mr. Trump has made the tariffs a cornerstone of his economic and foreign policy since returning to the White House. He claimed the federal trade deficit was a national emergency to justify his import taxes.

The Constitution gives Congress the exclusive power to impose tariffs on imports, but Congress has delegated its authority in recent decades by passing several laws allowing the executive branch to impose the levies in certain circumstances. Two lower courts, though, have said that Mr. Trump’s tariffs fall outside what has been authorized by lawmakers.

Costco says the lawsuit is necessary to make sure it can get refunded if the Supreme Court rules against the Trump administration. It is also asking the United States Court of International Trade to block the collection of further tariffs.

The lawsuit claims Costco is facing imminent and irreparable harm because goods for which it paid duties are anticipated to be “liquidated” by United States Customs and Border Protection agency as early as December 15.

The agency automatically finalizes tariff determinations 314 days after the goods enter the United States, effectively locking the payments in permanently. Costco says that it could become impossible to obtain refunds if the payments are locked. Costco’s lawsuit claims the federal agency has refused to extend the deadline.

Costco didn’t disclose in the case — Costco Wholesale Corp. v. Customs and Border Protection —  how much the tariffs have cost it so far.

Several conservative Supreme Court justices seemed skeptical of the Trump administration’s rationale for levying his “Liberation Day” tariffs during an hours-long, high-stakes hearing last month. The petitioners, a group of small businesses, claim President Trump’s use of reciprocal tariffs is an overstep of his powers and should be struck down.

President Trump asked for an expedited ruling in the case and the high court could release its decision before the end of the year.

Costco isn’t the first big company to file a tariff refund lawsuit, but it is the largest retailer to sue. Revlon Consumer Products, Bumble Bee Foods, and Kawasaki Motors Manufacturing have also filed suit asking for refunds, according to the Wall Street Journal.

“The economic consequences of the failure to uphold President Trump’s lawful tariffs are enormous and this suit highlights that fact,” White House spokesman Kush Desai said in an emailed statement. “The White House looks forward to the Supreme Court’s speedy and proper resolution of this matter.”

Costco didn’t immediately respond to a request for comment.