News media company CNN has terminated three of its employees for coming to the office unvaccinated against the Covid-19 last week, according to a memo sent to staff internally on Thursday.

In the note seen by Reuters, President Jeff Zucker told employees that the company has a zero-tolerance policy on such instances and required its employees to be vaccinated to come to office or to work on field with other employees.

"Everyone from news, sports and studios who comes in now and going forward must be vaccinated. We have been clear about this for months, so there should be no confusion," according to the memo.

Showing proof of vaccination may now become a formal part of the process to enter office, CNN said, as against an honour system earlier.

Besides, CNN has decided to postpone the Sept. 7 return date in the U.S. to around mid-October due to the increase in Covid-19 cases across the country and has mandated masks in its Los Angeles, Washington DC, and Atlanta workspaces, Zucker said in the note.

It, however, didn't disclose the office location where the incident took place.

Several companies across the U.S. have changed their plans on vaccinations, masking and return to office due to the resurgence of Covid-19 cases in the country and the announcement of new guidance from the U.S. Centers for Disease Control and Prevention that requires fully vaccinated individuals to wear masks.

CNN currently has most of its offices open for employees who want to work there voluntarily, provided they are fully vaccinated.