The U.S. National Labor Relations Board has filed a complaint against SpaceX, accusing it of illegally firing eight employees who participated in writing a letter criticizing the company’s CEO, Elon Musk. Musk’s behavior was described by employees as “a frequent source of irritation and embarrassment.”

The complaint further alleges that SpaceX created the impression that it was surveilling the employees by showing one of them screenshots of a Signal group chat in which several of his other colleagues were participating. The open letter at the center of the case called attention to Musk’s “malicious behavior on Twitter.” Employees expressed concern over crude jokes Musk made in connection with sexual abuse allegations. In the letter, the employees asked the company’s management to condemn Musk’s behavior.

Employees circulated the letter within the company in 2022. Five employees were reportedly fired the very next day, and another four were fired during July and August“At SpaceX, the rockets may be reusable, but the people who make them are treated as expendable,” Paige Holland-Thielen, one of the fired employees, told The Times. “I hope these allegations hold SpaceX and its management accountable,” she added.

The case is scheduled to be heard by an administrative judge on March 5. If the National Labor Relations Board determines that SpaceX violated labor laws, it can order the company to rehire the workers and provide them with appropriate back wages.