The company said it has a "zero-tolerance policy" for reporting to the office without vaccination against Covid-19.
CNN has fired three employees who violated company policy by coming to work unvaccinated against Covid-19.
In a memo to staff members about the firing, CNN chief Jeff Zucker reminded employers that vaccines were mandatory if they report to the office or out in the field where they come into contact with other employees.
"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," Zucker said.
Zucker added he understood that workers "are all feeling a mix of anticipation, anxiety, frustration, confusion and exasperation” and urged colleagues to look out for one another.
The broadcaster also confirmed a planned company-wide return to the office has been delayed until at least October.
The memo was originally tweeted out by CNN media reporter Oliver Darcy, but CNN did not provide any details about where the employees were based or what their roles were.
CNN are not alone in their company policy on vaccinations with Google, Disney and the NFL also making vaccines mandatory for staff before they return to work.
US President Joe Biden has also mandated that all federal employees either take the vaccine or else comply with a weekly testing programme.
