The approach to vaccination has been wildly different for each of the U.S.-based carriers. While United was the first to require inoculation, they were quickly joined by Hawaiian Airlines and Frontier Airlines. American Airlines offered incentives to employees, while Delta Air Lines added a health insurance surcharge for those who refuse to get vaccinated.

Once president Joe Biden signed an executive order requiring all companies with over 100 employees and government contractor companies to mandate vaccines, major companies and airlines were all affected. To maintain their government contracts, American, Alaska and JetBlue are now requiring their workers to get the shot.

In a internal memo leaked to Twitter, American chief executive Doug Parker and president Robert Isom announced that because the Fort Worth-based carrier participates in the City Pair Program, the Civil Reserve Air Fleet program and Department of Defense cargo contracts, the company has no choice but to comply. The executives made their position clear: “Team members who choose to remain unvaccinated will not be able to work at American Airlines.”

Breaking: @AmericanAir says federal vaccine mandate will apply to all U.S-based employees pic.twitter.com/JYdkx2McDa
— davidshepardson (@davidshepardson) October 1, 2021

Alaska and JetBlue will also follow suit, noting that their employees must be fully vaccinated by December 8, 2021. Because there is no alternative in the executive order, those who wish to remain unvaccinated cannot wear face coverings and submit to weekly testing. Instead, they will either have to get vaccinated or look for work elsewhere.

The moves comes as the White House continues to pressure carriers to set a vaccine mandate for all employees. Reuters reports the executive branch’s COVID-19 coordinator spoke to leaders at American, Delta Air Lines and Southwest Airlines to reinforce the need for an internal mandate.