United Airlines Is Firing Workers Over Vaccine Noncompliance

United Airlines said it would terminate about 600 employees for refusing to comply with its vaccination requirement, putting the company at the forefront of the battle over vaccine mandates as the economy moves through a bumpy pandemic recovery.

The airline also said that 99 percent of its U.S. work force of 67,000 had been vaccinated, a sign that mandates can be an effective way for companies to prod their employees to get shots.

More large companies have announced vaccine requirements as the government puts increasing pressure on them to help the country increase its inoculation rate. This month, President Biden mandated that all businesses with 100 or more workers require their staff to be vaccinated or face weekly testing, helping propel new corporate vaccination policies.

Some companies are still trying to encourage their employees with a mix of incentives and deterrents, but many others have made vaccination compulsory as a condition of work. On Wednesday, AT&T said it was extending its vaccination requirement to tens of thousands of unionized employees.

In August, United Airlines became the first U.S. carrier and one of the first large corporations to mandate a vaccine for Covid-19.

“This was an incredibly difficult decision but keeping our team safe has always been our first priority,” Scott Kirby, United’s chief executive, and Brett Hart, its president, said in a memo sent to the staff on Tuesday.

On Wednesday, a spokeswoman confirmed that the company had already begun its process to terminate 593 U.S.-based employees who declined to be vaccinated.

“We will work with folks if during that process they decide to get vaccinated,” the spokeswoman said. United Airlines did not give a timeline for the termination process or a breakdown of the job categories of the fired workers.

United has said that unvaccinated workers can request an exemption based on religious or medical reasons. It had planned to place exempt workers on leave, in many cases unpaid, starting Saturday. But the airline postponed the decision, until Oct. 15, pending a lawsuit filed by six employees, the International Association of Machinists and Aerospace Workers union said in a statement on Monday.

Roughly 350 workers in customer service, storekeeper and baggage service positions have not reported proof of vaccination to the airline, said Michael Klemm, district president of the machinists union.

“We’re not in agreement with United’s position,” he said. “We plan, through a collective bargaining agreement, to grieve this process.”

A spokesman for the union representing flight attendants said about 100 of its members had not reported proof of inoculation. “We are demanding that the company give the flight attendant every benefit and make sure they’ve researched every issue for every flight attendant before they’re terminated,” said Jeff Heisey, the secretary-treasurer of the union, the United Master Executive Council.

Any company is within its legal right to require employees to be vaccinated, barring any conflicting disability or religious belief, the U.S. Equal Employment Opportunity Commission has ruled.

The Occupational Safety and Health Administration has not provided details in response to Mr. Biden’s announcement for a nationwide mandate. The regulation is expected to be challenged in court by employers and perhaps even some states.

OSHA has the authority to quickly issue a rule, known as an emergency temporary standard, if it can show that workers are exposed to a grave danger and that the rule is necessary to address that danger. The rule must also be feasible for employers to enforce.

“There’s public policy in favor of vaccine mandates, so it’s almost impossible for an employee to argue that it’s against public policy to terminate them as long as the employer provided exemptions on medical and religious grounds,” said Aditi Bagchi, a labor law professor at Fordham University School of Law.

In early August, United announced that all its employees would be required to provide proof of vaccination within five weeks of a vaccine’s full approval by the Food and Drug Administration, or by Oct. 25, whichever came first. The F.D.A. in late August granted full approval to Pfizer-BioNTech’s coronavirus vaccine for people 16 and older. At the time, United warned that it would fire employees who did not follow the new policy.

Other airlines have taken different measures to encourage employees to get inoculated. Delta Air Lines announced last month that it was adding a $200 monthly surcharge on its health care plan for unvaccinated employees. The company has also said that it requires new employees to be vaccinated, but that existing employees are exempt. American Airlines said it was “not putting mandates in place” for employees or customers.

Other industries are enforcing vaccination requirements. Hospitals across the country have fired health care workers for refusing to comply with vaccination requirements, and in early August, CNN said it had fired three employees who violated its coronavirus safety protocols by going to the office unvaccinated.