Several former SpaceX employees filed unfair labor practice charges against the company with the National Labor Relations Board on Wednesday, alleging they were fired for raising concerns about CEO Elon Musk.

The former employees were part of a group that sent a letter to SpaceX’s executive team about Musk, expressing their concerns about recent sexual harassment allegations against the CEO and his behavior on Twitter, according to the employees’ attorneys.

The group reportedly said in the letter that Musk’s behavior was hurting SpaceX’s reputation and culture and called on the company to condemn Musk’s “harmful” activity on Twitter and hold its leadership accountable. 

Five employees were fired the day after the letter went out, with four more being fired within the next two months, the attorneys alleged.

“Part of what was supposed to be so great about SpaceX was that any person at any level could escalate issues to leadership and be taken seriously and treated with respect,” former employee Paige Holland-Thielen said in a statement. 

“We drafted the letter to communicate to the executive staff on their terms and show how their lack of action created tangible barriers to the long term success of the mission,” she added. “We never imagined that SpaceX would fire us for trying to help the company succeed.”

Musk has been embroiled in controversy since he took over Twitter three weeks ago. The billionaire laid off nearly half of the social media company’s workforce in his first week and recently suggested that the company was still “overstaffed.”

The Twitter CEO told his remaining staff that they would not be permitted to work remotely and said they needed to be willing commit to a “hardcore” work environment. Several top executives have resigned amid the chaos.

Musk’s attempted changes to the social media platform itself have also garnered criticism, with the CEO temporarily rolling back his plans to allow users to pay for verification through a subscription service after an initial launch of the revamped service led to a number of accounts impersonating high-profile figures and companies.