DETROIT >> The United Auto Workers Union said today it has filed charges with the National Labor Relations Board against Donald Trump and Tesla CEO Elon Musk over attempts to threaten and intimidate workers. The action came after Musk and Trump held a two-hour conversation on social media platform X on Monday night, during which the two discussed workers walking off the job to go on strike.

“You’re the greatest cutter,” Trump said during the conversation. “I mean, I look at what you do. You walk in, you just say: ‘You want to quit?’ They go on strike – I won’t mention the name of the company – but they go on strike. And you say: ‘That’s okay, you’re all gone.’”

Under federal law, workers cannot be fired for going on strike, and threatening to do so is illegal under the National Labor Relations Act, the UAW said in a statement.

The UAW has endorsed Vice President Kamala Harris in her bid for U.S. president. She met with union officials and workers last week near Detroit.

“Both Trump and Musk want working class people to sit down and shut up, and they laugh about it openly. It’s disgusting, illegal, and totally predictable from these two clowns,” UAW President Shawn Fain said in a statement today.

The NLRB has limited power to punish unlawful labor practices. In cases involving illegal threats, the board can order employers to cease and desist from such conduct and to post notices in the workplace informing workers of their rights. Unions can also use favorable rulings from the NLRB to engage workers they are trying to organize.

Fain filed separate complaints against Musk and Trump with the NLRB, claiming both men had made statements suggesting they “would fire employees engaged in protected concerted activity, including striking.” The complaints did not provide further detail.

The Harris and Trump campaigns did not immediately respond to requests for comment. Musk also did not respond to a request for comment. The UAW led a six-week strike against Detroit’s Big Three automakers last autumn, in which workers at Ford Motor, General Motors and Jeep maker Stellantis walked picket lines across the country.

The union won record contracts, which included a 25% general wage increase over the life of the agreement, along with cost-of-living adjustments. The wins equated to substantial labor expenses for the Detroit carmakers, auto executives said, an added challenge as they race to slim costs to stay competitive with Tesla. Musk, who has endorsed Trump for president, has had numerous run-ins with the labor board. His rocket company SpaceX is currently challenging the entire structure of the agency in a pair of pending lawsuits. Those cases stemmed from NLRB complaints accusing SpaceX of firing engineers who were critical of Musk and forcing employees to sign severance agreements with unlawful terms.

In March, a U.S. appeals court upheld an NLRB decision that said Musk illegally threatened Tesla employees by tweeting in 2018: “Nothing stopping Tesla team at our car plant from voting union … But why pay union dues & give up stock options for nothing?”

The electric vehicle maker is separately facing allegations from the board that it illegally discouraged unionizing at a Buffalo, New York, assembly plant. Last year, an appeals court threw out a labor board decision that said Tesla broke the law by barring factory workers from wearing UAW T-shirts.