At stake is some US$166 billion in revenue. A refunds system handled by US Customs and Border Protection (CBP) has already begun to process repayments.

Last month, the CBP said in a court filing that it was on track to process about US$85 billion in repayments, with US$20.6 billion approved for disbursement.

But the latest appeal could potentially impact this operation.

After returning to the White House last year, President Donald Trump moved swiftly to impose sweeping tariffs on allies and competitors alike, tapping the International Emergency Economic Powers Act to target different countries with different rates.

In February this year, the high court ruled that Trump had exceeded his authority in imposing these duties.

A judge of the Court of International Trade has since ruled that refunds should take place, although giving room for the CBP to comply with the order.

The agency estimated in March that more than 330,000 importers could be eligible for repayments.

Hundreds of companies have sought to get their money back, including small businesses and major firms like delivery and freight giant FedEx and warehouse retailer Costco.

Trump, however, has said that he would remember US companies that did not seek tariff refunds, signalling that he might view them more favourably.

Since the Supreme Court ruling – which did not affect Trump’s sector-specific tariffs – the US leader has tapped separate authorities to slap a new 10% tariff on imports.

This is temporary, however, as US officials move to enact more lasting duties.