SpaceX fires at least 5 employees after internal letter criticizes CEO Elon Musk

SpaceX has fired at least five employees involved in circulating a letter around the company that was critical of CEO Elon Musk, two people familiar with the company told CNBC.

The open letter, first reported by The Verge, was circulated and signed by an unknown number of SpaceX employees earlier this week. The letter was addressed to company executives, according to media reports, and described the billionaire's public behavior as "a frequent source of distraction and embarrassment" for SpaceX employees.

Musk is the controlling shareholder of the privately held company, with his trust owning about 78% of SpaceX's voting shares as of last year. The CEO has created an often eccentric persona in public spheres, particularly on Twitter where he offers commentary and updates on SpaceX and his electric vehicle company, Tesla.

Musk has often said he uses Twitter to express himself, comparing his use of the service to how "some people use their hair," and is seeking to acquire the social media company.

Musk said during a Twitter all-hands meeting on Thursday that free speech is critical to users of the platform – even if a company is under his private ownership, like SpaceX.

The internal SpaceX letter also referenced recent sexual misconduct allegations against Musk, reported by Business Insider last month. The report said Musk sexually harassed a SpaceX flight attendant during a private flight, and that the company paid the employee $250,000 for her silence.

SpaceX President and COO Gwynne Shotwell defended Musk after the misconduct allegations, writing in an email to employees that she believes "the allegations to be false."

The New York Times first reported the SpaceX firings. SpaceX did not immediately respond to CNBC's request for comment.