News network CNN has dismissed three employees who went into work unvaccinated against Covid-19.
It is one of the first examples of a US company sacking workers for breaching its vaccination mandate.
CNN president Jeff Zucker told staff members of the dismissals in a memo sent on Thursday.
He reminded employees that the coronavirus vaccine is mandatory if they report to the office or out in the field where they come into contact with other employees.
“Let me be clear. We have a zero tolerance policy on this,” he added.
The US has recently seen a surge in the delta variant.
In May, the US government made it legal for companies to require employees in the workplace to be vaccinated.
Many large companies such as Google and Facebook have indicated that they will implement this requirement when offices fully reopen.
CNN offered no details about the fired employees or where they were based.
Most of the company’s offices are already open on a voluntary basis, although Mr Zucker said more than a third of news staff have returned.
Proof of vaccination has been left to an honour system, he said, but that may change in coming weeks.
He added that masks will be required in Atlanta, Washington and Los Angeles offices when people are not eating, drinking or in an enclosed private space.
Even in offices where mask-wearing is not mandated, people should do what feels comfortable to them “without any fear of retaliation or judgment from co-workers,” he added.
The CNN memo also said a planned company-wide return to the office on September 7 will be delayed until at least early to mid-October.
Other media companies have been making similar decisions because of the rise in Covid cases.
President Joe Biden has ordered two million federal workers to provide proof that they have had the jab or undertake compulsory testing and mask-wearing.
