SpaceX is facing a lawsuit from the National Labor Relations Board (NLRB), accusing the company of unlawfully firing employees after they wrote an open letter criticizing CEO Elon Musk.

Last year, a group of SpaceX employees drafted an open letter expressing concern that Musk's behavior was "often distracting and embarrassing." At the time, Musk was trying to acquire Twitter, which he later renamed X after taking control of the company. SpaceX subsequently fired the employee who helped write the letter.

In a complaint filed Wednesday, the NLRB accused SpaceX of questioning employees about their involvement in writing the letter and telling employees not to discuss the interviews. NLRB spokesperson Kayla Blado told Reuters that SpaceX violated workers' federal rights to collectively fight for better conditions.

The labor agency claimed that SpaceX "created the impression of surveillance" by reading and showing screenshots of messages between employees, adding that the company tried to prevent employees from distributing the open letter. SpaceX also allegedly "asked employees to resign and threatened to fire them" if they participated in organized activities.

The NLRB requires SpaceX to post a notice about employee rights within 120 days and wants the company to write an apology letter to every fired employee. An NLRB administrative law judge (ALJ) will hold a hearing on March 5, 2024, provided SpaceX does not attempt to settle the charges. Whatever the judge decides can be appealed to the board and to the federal appeals court.