United Airlines (UAL) began firing some unvaccinated U.S.-based workers on Tuesday. However, the airline agreed to postpone plans to put another group of unvaccinated workers on mostly unpaid leave after they'd applied for medical or religious exemptions to its mandatory COVID-19 vaccination policy.

Six of those exempted workers are challenging United's policy in a federal lawsuit in Texas, which employment lawyers say is likely to turn on the nature of the alternatives that United offered to employees who sought exemptions.

"You can have a mandatory vaccination policy; however, employees may be entitled to a reasonable accommodation based on either a sincerely held religious belief and or a disability, if it doesn't cause an undue burden on the employer," LaKeisha Caton, an attorney with Pryor Cashman, told Yahoo Finance.

An 'impossible choice' under United's COVID vaccine policy

The lawsuit, a purported class action that the plaintiffs estimate to include more than 2,000 workers, is being brought by two captains, a flight attendant, a customer service representative, a station operations representative, and an aircraft technician. The group seeks a preliminary injunction and a permanent injunction that would stop United from carrying out plans to place them on indefinite periods of paid or unpaid leave. 

“United’s actions have left plaintiffs with the impossible choice of either taking the COVID-19 vaccine, at the expense of their religious beliefs and their health, or losing their livelihoods," the suit states.

The employees claim United failed to comply with the Americans with Disabilities Act (ADA) and Title VII of the Civil Rights Act by failing to engage in legally required communications with employees who are granted medical or religious exemptions. The suit also claims United violated federal law by enforcing its policy against unvaccinated workers who have antibodies against COVID-19, and by defaulting exempted workers into unspecified terms of paid or unpaid leave.

“Nothing in the policy suggests that employees will be terminated for requesting or receiving an exemption,” the complaint states, arguing that the unspecified terms, accompanied by a loss of health insurance and other benefits, is tantamount to being fired.

United says workers granted a medical exemption could use paid sick leave, and workers granted a religious exemption would receive unpaid leave. The complaint alleges that at least one medically exempted worker was instead offered unpaid leave, and that additional employees were prevented from submitting for both medical and religious exemptions.

Since the lawsuit was filed, United halted its plan to start placing workers who submitted applications for accommodations on leave.

In response to the complaint, a United spokesperson said the company would "continue to vigorously defend" its policy. "Vaccine requirements have been around for decades and have served to keep airline employees and customers safe," the spokesperson added.

In arguing against the request for an injunction, United said the ADA doesn't allow such an extraordinary solution and that the workers could instead get money damages if they proved intentional discrimination. Plaintiffs, for their part, say their loss of income would lead to serious consequences, including for one plaintiff, homelessness.

Are United's vaccine accommodations reasonable?

For now, University of Pennsylvania law professor Jasmine Harris said the judge is faced with deciding whether to grant the exempt workers' more immediate request to stop United from cutting off their income and benefits. Whatever the judge's decision, she said, the legal analysis will offer a preview of the case's core legal questions.

Those questions include whether under the ADA or Title VII the accommodations would impose an "undue hardship" on United, and whether whether the accommodations are considered reasonable.

Syracuse University law school professor Doron Dorfman told Yahoo Finance that the indefinite nature of United's offer to keep exempt workers on leave could pose a challenge for its "reasonableness" defense.

"If I were to advise United, I would just do it year by year, or for six months," Dorfman said, explaining that a judge might find longer terms unreasonable.

Caton made a similar conclusion, explaining that a blanket default to unpaid leave could potentially indicate the company didn't meet its legal burden to engage in more robust communications with exempt workers.

"I'm not surprised that they took a pause on that," Caton said, "because practically speaking for these employees...automatically put on unpaid leave, that raises the question: Is that really a reasonable accommodation? If you're put on indefinite unpaid leave that's, for all practical purposes, akin to a termination."

United's obligations are minimal

Experts stress that religious and medical exceptions pose hurdles for the workers too because of legal limitations that protect employers from undue hardship.

Religious-based accommodations, Dorfman explains, impose the most minimal requirements on employers, where the standard the employer must meet is even lower than under the ADA.

Under the standard, courts have upheld employers' rights to avoid accommodations such as those that compromise workplace safety, are too costly, and decrease workplace efficiency.

"Basically what it means is that an employer does not need to do anything except the minimum to accommodate a person for religious accommodation," Dorfman said.

However, Harris notes that employers rarely find a winning argument if they rely solely on the position that an accommodation is too costly.

Medical accommodations, meanwhile, are additionally limited to workers with a qualifying condition — meaning one that directly impairs their ability to comply with the policy.

"The definition of disability is actually fairly broad under the ADA," Caton said, explaining that it can include a variety of medical conditions. "That being said, you have to show that you're disabled and that that disability entitles you to reasonable accommodation from being vaccinated. So it's going to be problematic for these employees if they can't show that, because that burden is on them."

United will likely argue that there's no reasonable accommodation at all that would allow the workers to perform their essential job functions, according to Harris. An unvaccinated worker with no proven immunity, and who needs to interact with other workers or the public, for example, could threaten a safe work environment.

United announced its policy to U.S.-based workers on Aug. 6, and later confirmed that proof of full vaccination would be required by Oct. 31.

On Thursday, United said that 99% of its U.S.-based employees chose to become vaccinated, excluding those who submitted for an accommodation. Multiple news reports on Thursday also said the company's number of unvaccinated U.S.-based workers facing termination under its policy had dropped from 593 to 320. A hearing on the preliminary injunction is scheduled for Oct. 8.

Alexis Keenan is a legal reporter for Yahoo Finance. Follow Alexis on Twitter @alexiskweed.

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