Donald Trump said he will fire Federal Reserve Chair Jerome Powell if he does not step aside when his term expires next month.

Powell’s tenure as chair expires on May 15. Trump’s pick for a replacement, Kevin Warsh, has yet to be confirmed by the Senate and the full chamber. That leaves the potential for Powell to remain in place as chair “pro tempore,” per Fed regulations.

Powell confirmed at a press briefing in March that if Warsh isn’t confirmed by the Senate by May 15, Powell would remain as Fed chair “pro tem” in the interim. “That’s what the law calls for. That’s what we’ve done on several occasions,” Powell said at the time.