What may be the biggest battle yet in Donald Trump's trade war is about to begin. The Trump administration heads to the US Supreme Court on Wednesday, facing off against small businesses and a group of states who contend most of the tariffs it has put in place are illegal and should be struck down.

If the court agrees with them, Trump's trade strategy would be upended, including the sweeping global tariffs he first announced in April. The government would also likely have to refund some of the billions of dollars it has collected through the tariffs, which are taxes on imports.

The final decision from the justices will come after what could be months of poring over the arguments and discussing the merits of the case. Eventually they will hold a vote.

Trump has described the fight in epic terms, warning a loss would tie his hands in trade negotiations and imperil national security. On Sunday, the president said he will not attend the hearing in person as he did not want to cause a distraction.

I wanted to go so badly... I just don't want to do anything to deflect the importance of that decision, he said. It's not about me, it's about our country.

Trump previously said that if he does not win the case the US will be 'weakened' and in a 'financial mess' for many years to come.

The stakes feel just as high for many businesses in the US and abroad, which have been paying the price while getting whipped about by fast-changing policies. Trump's tariffs will cost Learning Resources, a US seller of toys made mostly overseas and one of the businesses suing the government, $14m this year. That is seven times what it spent on tariffs in 2024, according to CEO Rick Woldenberg.

Legal analysts say it is hard to predict the justices' answer, but a ruling siding with Trump will give him and future White House occupants greater reach. By declaring an emergency under the law, Trump can issue immediate orders and bypass longer, established processes.

Opponents say the law authorises the president to regulate trade but never mentions the word 'tariffs', and they contend that only Congress can establish taxes under the US Constitution. Members of Congress from both parties have asserted the Constitution gives them responsibility for creating tariffs.

Three lower courts have ruled against the administration. After the Supreme Court hears arguments on Wednesday it will have until June to issue its decision, although most expect a ruling to come by January. Whatever it decides has implications for an estimated $90bn worth of import taxes already paid, roughly half the tariff revenue the US collected this year through September.

The case has already complicated the White House's trade deals and businesses are left uncertain as they await the court's ruling. The future of various industries and companies hangs in the balance as the legal showdown unfolds.