The US news agency CNN has fired three employees for going to office without being vaccinated against Covid, US media say.
It is one of the first examples of US company employees dismissing their employees for violating company coverage guidelines.
It is legal in the United States for companies to require employees to be vaccinated.
Many large companies - including Facebook and Google - say they will need workers to be vaccinated when the offices are fully opened in the coming months.
CNN CEO Jeff Zucker cited the dismissal in a company's internal notification posted Thursday and viewed by several US media outlets.
Vaccination is mandatory for anyone reporting outside, working with any other staff or entering the office, is quoted as saying in the notice.
"Let me be clear - we have a policy of not loosening the noose on this issue," Mr. Zucker, chairman of news and sports for WarnerMedia, was quoted as saying.
In May the US government said it was legal for employers to require office-going workers to be vaccinated against Covid-19.
Major airlines Delta and United Airlines require new staff to show proof of coverage, while investment bank Goldman Sachs wants its employees to disclose their coverage status, although it does not require staff to be vaccinated, the AP reports.
President Biden has ordered two million central government employees to show immunizations or undergo mandatory tests and wear bracelets
