SpaceX has banned Zoom, saying that it is unsafe.
Elon Musk's private space company said that employees could no longer use the video conferencing app because of "significant privacy and security concerns".
Instead, it advised people working from home to use more traditional methods to communicate with each other, according to a memo first reported by Reuters.
The use of Zoom and other video conference apps has surged in recent weeks, as lockdowns across the world have forced people to stay away from their usual places of work and study.
That has left aerospace companies like SpaceX – which works on highly classified technology and missions from other organisations such as Nasa – rushing to ensure they can still work without compromising national security.
In an email dated March 28, SpaceX told employees that all access to Zoom had been disabled with immediate effect.
"We understand that many of us were using this tool for conferences and meeting support," SpaceX said in the message. "Please use email, text or phone as alternate means of communication."
Those more traditional methods come with their own security problems. Neither traditional email or texts are end-to-end encrypted, meaning that they can be intercepted and read as they are passed between different people.
Two people familiar with the matter confirmed the contents of the mail, Reuters reported. A representative for SpaceX, which has more than 6,000 employees, did not respond to a request for comment.
NASA, one of SpaceX's biggest customers, also prohibits its employees from using Zoom, said Stephanie Schierholz, a spokeswoman for the U.S. space agency.
The FBI's Boston office on Monday issued a warning about Zoom, telling users not to make meetings on the site public or share links widely after it received two reports of unidentified individuals invading school sessions, a phenomenon known as "zoombombing."
Investigative news site The Intercept on Tuesday reported that Zoom video is not end-to-end encrypted between meeting participants, and that the company could view sessions.
Zoom did not immediately respond to requests for comment on SpaceXâs decision, but it has been advising users to use all the privacy functions on its platform.
As a defence contractor, California-based SpaceX has been classified as an essential business, allowing it to stay open through shutdowns that are in effect in California and Texas, the development and testing hub for its Starship rocket that could be used to get to the moon and Mars and send national security satellites to space.
Additional reporting by Reuters