SpaceX, the rocket and satellite manufacturer, has been accused by a US labor agency of unlawfully terminating eight employees for circulating a letter criticizing CEO Elon Musk. The National Labor Relations Board (NLRB) issued a complaint asserting that SpaceX violated the workers’ rights under federal labor law to collectively advocate for improved working conditions.

The letter, sent to SpaceX executives in June 2022, focused on Elon Musk’s tweets since 2020, many of which were sexually suggestive. The employees contended that Musk’s statements did not align with the company’s policies on diversity and workplace misconduct and called on SpaceX to condemn them.

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The complaint also accuses SpaceX of interrogating employees about the letter, disparaging those involved, and threatening to fire workers engaging in similar activities. SpaceX has not yet responded to the allegations.

The NLRB’s general counsel brings cases to the five-member board appointed by the president. If SpaceX does not settle, the case will go before an administrative judge, with a hearing scheduled for March 5. If found in violation of labor law, SpaceX may face penalties, including reinstating workers and providing back pay.

This case is the latest in a series accusing companies led by Elon Musk of violating employees’ rights. In November, Reuters reported over 600 previously unreported workplace injuries at SpaceX facilities. In October, the NLRB accused X (formerly Twitter), owned by Musk, of illegally firing an employee over tweets challenging the company’s return-to-office policy. Tesla, another company led by Musk, has faced NLRB complaints amid a union organizing campaign and lawsuits alleging widespread race discrimination at its factories. Tesla has denied tolerating discrimination.