The United Auto Workers union said on Tuesday it has filed charges with the National Labour Relations Board against Donald Trump and Tesla owner Elon Musk over attempts to threaten and intimidate workers.
The action came after Mr Musk and Mr Trump held a conversation on social media platform X on Monday night, during which the Republican presidential hopeful complimented Mr Musk's ability to cut costs by saying he would not tolerate workers going on strike.
“You're the greatest cutter,” Mr 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 OK, you're all gone.'”
Mr Musk did not comment but responded to Mr Trump's comments with a chuckle.
Under federal law, workers cannot be fired for going on strike and threatening to do so is illegal under the National Labour Relations Act, the UAW said.
The UAW endorsed Democratic presidential candidate and Vice President Kamala Harris in July and has encouraged its nearly 400,000 members to vote for her over Mr Trump, especially in battleground states like Michigan, where the UAW is based.
It represents thousands of workers throughout battleground states in the upper Midwest. Pennsylvania, Wisconsin and Michigan are expected to be among the most important swing states that will determine the winner of the November election.
Union president Shawn Fain and Mr Trump have crossed swords in the past.
“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,” Mr Fain said in a statement on Tuesday.
The UAW cut a video of Mr Trump praising Mr Musk and posted the clip on social media sites, writing to its more than 125,000 followers on X: “He’s for the billionaires. Not for you. Donald Trump is a scab.”
Meanwhile, Mr Trump has called for the union leader to be fired, saying he is responsible for US car manufacturing becoming weaker.
Mr Fain filed separate complaints against Mr Musk and Mr Trump with the NLRB, claiming both men had made statements suggesting they “would fire employees engaged in protected concerted activity, including striking”.
The UAW led a six-week strike against Detroit's Big Three car makers last autumn, in which workers at Ford, General Motors and Jeep maker Stellantis walked picket lines across the country.
The union won record contracts, which included a 25 per cent general wage increase over the life of the agreement.
Mr Musk, who has endorsed Mr Trump for president, has had numerous run-ins with the labour board: his rocket company SpaceX is currently challenging the entire structure of the agency in a pair of pending lawsuits, and in March, a US appeals court upheld an NLRB decision that said Mr Musk had 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?”
Tesla is separately facing allegations from the board that it illegally discouraged unionising at a Buffalo, New York, plant. Last year, an appeals court threw out a labour board decision that said Tesla broke the law by barring factory workers from wearing UAW T-shirts.
