SpaceX has banned its employees from using Zoom for communication, in the latest challenge the popular videoconferencing app is facing.

In a memo seen by Reuters, SpaceX cites “significant privacy and security concerns” as the reason behind the ban. The memo goes on to say: “We understand that many of us were using this tool for conferences and meeting support. Please use email, text or phone as alternate means of communication.”

Zoom has been facing increasing scrutiny for its security and privacy, just as the app has become one of the most popular options for individuals sheltering in place and working from home. In short order, the app has been accused of not using end-to-end encryption, despite its marketing claims, as well as exposing users’ email addresses and phone numbers. Researchers have also discovered a serious security flaw in the Windows version of the app. New York Attorney General Letitia James is even looking into the company’s privacy practices.

The increased scrutiny of Zoom is a good reminder to companies that privacy and security should never be an afterthought. Instead, they should be a core feature, built in to an app or service from day one.