President-elect Donald Trump said on Monday that he plans to fire any federal employees who don’t physically return to their offices once his new administration begins and pledged to challenge in court a Biden-era agreement allowing for remote work.

“If people don’t come back to work, come back into the office, they’re going to be dismissed,” Trump said during a press conference at Mar-a-Lago, his private club and personal residence.

“Somebody in the Biden administration gave a five-year waiver of that, so for five years people don’t have to come back into the office,” he added. “It’s ridiculous. It was like a gift to a union, and we’re obviously going to be in court to stop it.”