The employees said on Thursday they were fired for being part of a group that had drafted and circulated a letter in June criticizing Musk and urging executives to make the firm’s culture more inclusive.
SpaceX did not immediately respond to a request for comment.
Reuters reported in June that SpaceX fired at least five employees after it found their involvement in the letter, which called Musk a “distraction and embarrassment” to the company.
The charges filed with the National Labor Relations Board allege that the owner of Starlink broadband service fired five employees the day after the letter was revealed, and four others in the two months after.
While two of the employees filed charges on their own, attorneys Anne Shaver and Laurie Burgess filed charges on behalf of six others, who are proceeding anonymously, the statement said.
Musk, also the head of electric-car maker Tesla, has been in the headlines over his acquisition of Twitter and attempts to rejigger the social media firm after he warned of a potential bankruptcy.