Numerous airlines have informed employees that the federal government will require them to get vaccinated. There is no other option than regular testing. The Biden administration decided to treat airlines like federal contractors and require that all employees receive 100% vaccination. This is in line with a pending OSHA rule.
Here's the American Airlines note for employees
The message is that since American Airlines like other U.S. airlines is a government-subsidized carrier, the government can impose employment policies.
American has cargo agreements with the government, receives subsidies for certain routes and gets revenue from Civil Reserve Air Fleet program (in return for planes that are used for flight approximately once a decade).
American pilots are going to have a lot of problems because they have over 4000 unvaccinated. Some pilots will be vaccinated. Some might retire early. American pilots are already in short supply.
In a recent meeting with employees, one American Airlines pilot made a valid point about federal rules not taking into account prior infection. A person who has had Covid-19 before and is given one shot of the mRNA vaccine is more protected than someone who has been double-vaccinated. The pilot could go to Johnson & Johnson if he so desired.
American Airlines offered a day off and $50 worth of Nonstop THanks credits (airline credit) but it didn't do enough. United's take a jab, or youe fired approach and Deltas surcharge for health insurance for the unvaccinated led them to have higher vaccination rates than United. This made them less susceptible to the new rules by the federal government.
Employees will need to be vaccinated before the holiday season begins on December 8. Although I don't think that this date will be extended, if sufficient compliance is not achieved then it may be delayed at the last moment. The Biden administration does not want to be blamed if Christmas travel is disrupted.