If you’re considering a COVID-19 vaccine mandate for your workplace—once vaccines are widely available, of course—here’s another thing to consider: the same foundation of legal precedent that backs flu vaccine mandates is weaker for the COVID-19 vaccine, according to one expert.

As COVID-19 vaccine distribution efforts ramp up in the United States—and experts predict anyone who wants a vaccine should be able to obtain one by the summer—the idea of mandating vaccinations in the workplace is gaining steam. Such mandates, theoretically, would create safer work environments, prevent workplace shutdowns and disruptions, and could even provide a competitive advantage: “We’re safer than our competitors because our workforce is fully vaccinated.”

In the past, employers have successfully mandated flu vaccines for all employees, particularly in the healthcare and elder care industries. Many of those mandates withstood legal challenges.

But there is a key difference between flu vaccines and COVID-19 vaccines, beyond which contagious disease they aim to curb. The flu vaccine (and many others) have passed through the normal regulatory and approval process set up by the U.S. Food and Drug Administration (FDA).

Not so with the ever-increasing number of COVID-19 vaccines, two (soon to be three) of which are available in the United States under emergency use authorization, said Dorit Rubinstein Reiss, a law professor at the University of California Hastings who specializes in vaccine law.

Vaccines made available under emergency use authorization have a weaker legal standing in disputes between employers and employees regarding workplace vaccine mandates, Reiss said.

“There is legal uncertainty over the emergency use authorization,” she explained during a panel Wednesday at Compliance Week’s “Compliance Considerations for the New Workplace” virtual summit. As a result, COVID-19 vaccination mandates may not hold up in court, at least not until the FDA’s emergency use authorization is lifted.

A typical vaccine approval takes two to three years, which includes clinical trials for all ages and tests its efficacy and safety on specific subsets of the population, like pregnant women. Currently, COVID-19 vaccines are only approved for adults. While clinical trials for children and pregnant women are underway, they have not been completed.

The accelerated—detractors would say rushed—process for approving COVID-19 vaccines is a big driver of hesitancy in the United States. Medical professionals argue potential adverse reactions to a vaccine are vastly outweighed by the vaccine’s protection against severe illness or even death posed by the disease itself. And vaccinating at least 70 percent of the population will help prevent the creation of more contagious COVID-19 variants like those identified in California, the United Kingdom, and South Africa.

Even still, COVID-19 workplace vaccine mandates open up employers to liability should an employee suffer an adverse reaction.

If your firm decides to head down the path of a COVID-19 vaccine mandate, there are several key exceptions in U.S. law. These exceptions are not unique to the COVID-19 vaccine but apply to all vaccines.

Employees can legally claim an exemption to a workplace vaccine mandate if they are classified as disabled under the Americans with Disabilities Act (ADA). Among the disabilities covered by the ADA is pregnancy, Reiss said.

Another way an employee could legally refuse a vaccine is with a firmly held religious belief, covered under the Civil Rights Act.

Many people may say they want a religious exception but are really expressing vaccine hesitancy, Reiss said.

“It’s really hard to measure sincerity,” she said. “A religious exemption is real, but it can be tricky.” Reiss said employers faced with an employee claiming a religious exemption should have the employee write a letter laying out their objection.

Employees who have a qualifying disability or a legitimate religious objection should be provided with reasonable workplace accommodations, Reiss said. In the case of an unvaccinated employee, accommodations might include allowing that employee to work from home, work a shift that exposes the employee to fewer people, or transferring him or her to a job that limits interaction with other employees or customers.

With flu vaccine mandates, courts have ruled in many cases employers can legally fire an employee who refuses to take the vaccine. The winning argument has often found an employee coming to work unvaccinated creates a workplace safety issue. But in such cases, the employer must show the steps taken to accommodate that employee and how the employee either refused to accept them or made requests too burdensome for the business to implement.

An interesting case of a vaccine mandate firing recently surfaced in New York, where a restaurant fired a female employee who said she would wait to get the vaccine because she was concerned about its potential effect on her ability to conceive a child.

“Being afraid is not a legal objection,” Reiss said. But she noted in this case, the restaurant did not offer up any workplace accommodations for the employee. In court, that would provide the employee with legal grounds to say the firing was unfounded.