United Airlines has told its 67,000 U.S.-based employees that they will need to be inoculated against COVID-19 by late October to stay on the job.

Citing "incredibly compelling" evidence that the vaccines are safe and effective, United CEO Scott Kirby announced the policy change on Friday. He said he understood that some employees would disagree with the mandate, according to AP.

The requirement is that all U.S. domestic employees of the airline be fully vaccinated by Oct. 25 — or five weeks from the date that any one vaccine gets full approval from the Food and Drug Administration, whichever comes first.

United is the first major U.S. carrier to require vaccination, although its decision follows similar moves in recent days by a number of other companies, including Walmart, with more than 2 million employees and Tyson Foods, which has 120,000 employees. Others include Facebook, Disney and Microsoft.

By contrast, American Airline CEO Doug Parker has told The New York Times that "we're not putting mandates in place."

The Air Line Pilots Association, which represents United's pilots, did not immediate respond to an NPR request for comment. However, on Thursday, the president of the Allied Pilots Association, which represents American's 15,000 pilots, reiterated the union's position on mandatory vaccines.

"APA's position remains the same: Whether a pilot elects to be vaccinated, or not, should be between the pilot and their medical provider, while any proposed vaccine mandate affecting our pilots would be subject to collective bargaining," APA President Eric Ferguson said in a letter to members that was shared with NPR.

Ferguson said that approximately 60% of the union's pilots had already opted to be vaccinated and encouraged its members to do so.

"We all want to put the COVID-19 pandemic behind us, and most of the scientific community agrees that vaccination provides a path to achieving that aim," he said.

In May, Delta Air Lines began requiring all new hires to show proof of vaccination and United followed suit the following month.

By contrast, American Airline CEO Doug Parker told The New York Times that "we're not putting mandates in place," the APA notes.

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