(Bloomberg) -- Southwest Airlines Co. can require its pilots to be vaccinated against Covid 19, while their union challenges the company’s requirement for the shot in court.

U.S. District Judge Barbara M.G. Lynn in Texas rejected the Southwest Airlines Pilots Association’s request to temporarily block the company mandate.

The union claims Southwest illegally changed work rules during the pandemic instead of negotiating with pilots, violating the Railway Labor Act, which governs airline-labor relations.

The pilots’ lawsuit is one of several filed against vaccine mandates by U.S. workers across multiple industries. United Airlines Inc. is battling a court challenge to its vaccine mandate. Delta Air Lines Inc. has imposed a $200-a-month charge for employees who are unvaccinated.

Southwest set a Nov. 24 vaccination deadline to comply with an executive order from President Joe Biden that all employees of federal contractors be fully vaccinated against Covid-19 by Dec. 8. Southwest, like most major U.S. carriers, holds contracts to carry federal employees and mail, and the U.S. government is its largest single customer.

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