SpaceX President Gwynne Shotwell said in the memo, which was seen by Bloomberg, that the company investigated the open letter and has terminated employees involved.

The situation “made employees feel uncomfortable, intimidated and bullied, and/or angry because the letter pressured them to sign onto something that did not reflect their views,” Shotwell said in the email. “We have too much critical work to accomplish and no need for this kind of overreaching activism.”

SpaceX didn’t immediately respond to a request for comment. The firings were reported earlier by the New York Times. A separate report from Reuters said at least five workers were fired.

See also: Elon Musk’s 180 on Tesla Job Cuts Did Damage to His Credibility

The upheaval is unusual for the rocket-launch and satellite-communications company, which Musk has maintained a tight grip over since founding it two decades ago. Space Exploration Technologies Corp., which has roughly 12,000 employees, serves private customers as well as government agencies including NASA.

Musk, also CEO of electric-vehicle maker Tesla Inc., regularly generates controversy, whether over his stances on overtly political topics, crass tweets or references to drug culture. Last month, Insider reported that SpaceX had paid an employee $250,000 to settle a claim she was sexually harassed by Musk in 2016. He has pushed back against the allegations, calling them “utterly untrue.”

Musk also is in a contentious process to acquire Twitter Inc. for $44 billion. He met with employees Thursday for the first time, where he said people should be allowed to say “pretty outrageous things” on the social-media platform.