President Donald Trump said on Wednesday the United States might have to "unwind" trade deals it clinched with South Korea and countries, if it loses a Supreme Court case on the legality of tariffs.

Trump, speaking to reporters at the White House, made the remarks at the start of his meeting with Polish President Karol Nawrocki.

Last week, a U.S. federal appeals court ruled that most of the tariffs imposed by Trump were "illegal," saying the International Emergency Economic Powers Act, which Trump cited as the legal basis for his trade agenda, does not give the president authority to impose tariffs.

Trump said losing that case would leave the United States far poorer, and could jeopardize trade agreements made in recent months.

"We made a deal with the European Union where they're paying us almost a trillion dollars," Trump said, adding that they'd have to unwind them.

Trump, however, added that his administration would prevail.