Electric carmaker Tesla Inc interfered with legitimate union organising and must read a notice to workers explaining their rights in a meeting requiring attendance from Chief Executive Elon Musk, a U.S. labour judge ruled on Friday.
The company committed a series of violations of the National Labor Relations Act in 2017 and 2018, Amita Baman Tracy, a California administrative law judge ruled in a court filing.
Among the violations of the law cited in the filing was a tweet sent by Musk in May 2018. "Nothing stopping Tesla team at our car plant from voting union. Could do so tomorrow if they wanted. But why pay union dues & give up stock options for nothing? Our safety record is 2X better than when plant was UAW & everybody already gets healthcare", Musk wrote in the tweet from last year.
The tweet amounted to "threatening employees" with loss of stock options if they vote in favour of the union, the judge said in her ruling on Friday.
The ruling has called on the electric carmaker to hold a meeting at its California assembly plant where either Musk or his agent must inform the workers that the National Labor Relations Board has concluded that Tesla broke the law.
Tesla did not immediately respond to a Reuters request for comment on Friday's ruling.
In the past, the company has been plagued by safety complaints brought by workers, allegations that Tesla denies. Workers have said that long hours and pressure to deliver vehicles quickly takes a toll, and some have pushed for a union.