Three CNN employees were fired for going to a company office without being vaccinated, the media firm’s CEO said in a memo that was leaked Thursday.

In an email to staffers about returning to work in person, Jeff Zucker warned that the company has a "zero-tolerance policy" about allowing people back who haven’t gotten the life-saving shots, according to Deadline.

"Thus far, we have left proof of vaccination to an honor system. While we have asked for attestation to your status via Passcard, it has not been mandatory to produce a vaccine card," Zucker wrote.

"In the past week, we have been made aware of three employees who were coming to the office unvaccinated. All three have been terminated. Let me be clear — we have a zero-tolerance policy on this."

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The email continues, "You need to be vaccinated to work in the field, with other employees, regardless of whether you enter an office or not. Period. We expect that in the weeks ahead, showing proof of vaccination may become a formal part of the WarnerMedia Passcard process. Regardless, our expectations remain in place."

The news station will also postpone its planned office return date from Sept. 7  to mid-October but honchos are "reluctant to put a specific date on it," Zucker wrote in the memo. 

Employees are currently allowed to work in the office on a voluntary basis — with masks required in Los Angeles, Washington, D.C., and Atlanta workspaces.

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"It goes without saying that even in places that we don’t mandate it, anyone who wants to wear a mask should absolutely do so. These decisions can be very personal for people – no two situations are the same," Zucker wrote. "Continue to take care of yourselves and each other."

Vaccine hesitancy has led to some delta variant breakthrough infections in the U.S. in recent weeks, according to health officials.