The UAW has filed a federal labor lawsuit against Donald Trump and Elon Musk, accusing them of attempting to threaten and intimidate workers.

The United Auto Workers union, which represents about 400,000 workers in the auto, aerospace and agriculture industries, announced on Tuesday that it had filed a federal labor lawsuit against Donald Trump and Elon Musk. The lawsuit follows what the UAW described as “an attempt to intimidate and threaten workers” during a conversation between Trump and Musk at X-Space on Monday night, in which Trump appeared to praise Musk, the owner of X-Space, for firing striking workers.

“Well, you’re the best firer,” Trump told Musk, the CEO of Tesla and SpaceX. “I mean, I look at what you do, you come in and you just say, ‘You want to quit?’ They start a strike. I won’t say the names of the companies, but they start a strike and you say, ‘All right, you all quit. You all quit.'” Musk did not respond specifically to Trump’s remarks, but laughed while the former president spoke and said he would be “happy to work with” him on a government efficiency committee.

According to the National Labor Relations Board, American workers, union or not, cannot be fired for participating in a protected strike. William B. Gould IV, a professor at Stanford Law School and former chairman of the National Labor Relations Board, said Trump’s comments “clearly state a position that violates the law.” Gould said Trump is acting on behalf of Musk’s company, and his comments could influence the company’s vote to unionize.

The NLRB must investigate the allegations and determine how to proceed if it finds the charges are warranted.

“This is exactly what they mean when they say Donald Trump is a strikebreaker. This is exactly what they mean when they say Trump is against the union cause,” UAW President Sean Fain said in a statement. “Both Trump and Musk want working class people to sit back and shut up, and they openly laugh at them. This is completely predictable, disgusting, and illegal from these two clowns.”

The UAW is endorsing Vice President Kamala Harris for president and has previously called Trump a “billionaire scab and stooge.” The union did not provide WIRED with a copy of the complaint it filed on Tuesday in response to a request from the NLRB; at press time it had not yet been posted on the NLRB’s website.

Musk’s companies have a blemished record when it comes to labor rights. Trump didn’t name Musk’s companies, but Musk is CEO of Tesla, SpaceX, Neuralink, and The Boring Company. Musk has said in the past that unionizing at Tesla would lead to the loss of stock options, and when he bought X (then Twitter), he drastically cut employees and eventually terminated the services of striking cleaners. SpaceX, meanwhile, is currently fighting the NLRB in court.

The UAW previously tried but failed to unionize Tesla workers. The union continues its efforts. Tesla and SpaceX did not respond to requests for comment. The Trump campaign did not respond to requests for comment.

Shortly after the UAW announced its charges, Musk posted on X, “The last two UAW presidents went to prison for bribery and corruption, and recent news suggests this guy will join them!” (Two former UAW presidents have been sentenced to prison in major corruption investigations, but they were not the two most recent union presidents.)