(NewsNation) — Former SpaceX employees say they were fired after writing an open letter criticizing the Twitter activity of the company’s CEO, Elon Musk, according to multiple reports.

According to coverage by Gizmodo, eight former employees filed unfair labor practices charges against the rocket manufacturer with the National Labor Relations Board. They claim SpaceX retaliated against them for writing the letter, calling their firing illegal.

Musk, who just took over as the chief executive at Twitter after buying the company, splits his time between Tesla and his other companies, including SpaceX.

Twitter has been a bit of a mess since the billionaire took the helm, cutting the company’s workforce in half, upending the platform’s verification system, sparring with users over jokes, and acknowledging that “dumb things” might happen as he reshapes one of the world’s most high-profile information ecosystems.

At the heart of the complaint, according to the New York Times, is Musk making light on Twitter of a news report that SpaceX settled a sexual harassment claim against him.

The open letter took issue with “inappropriate, disparaging, sexually charged comments on Twitter” by Musk, according to a Bloomberg report citing the NLRB filing.

Bloomberg reported that the complaint states the workers were fired “for engaging in the core concerted protected activity of speaking up against SpaceX’s failure and refusal to address the culture of sexism, harassment and discrimination.”

The open letter was written after a Business Insider story alleged Musk exposed himself to a flight attendant and asked her for sex in exchange for a horse.

Musk has denied the allegations, according to the report, including the claim that SpaceX paid the flight attendant $250,000.

The Associated Press contributed to this report.