A divided U.S. appeals court ruled on Friday that most of Donald Trump's tariffs are illegal, undercutting the Republican president's use of the levies as a key international economic policy tool.

The court allowed the tariffs to remain in place through Oct. 14 to give the Trump administration a chance to file an appeal with the U.S. Supreme Court.

The decision comes as a legal fight over the independence of the Federal Reserve also seems bound for the Supreme Court, setting up an unprecedented legal showdown this year over Trump's entire economic policy.