The legal issues alone are complicated. An employer can establish a mandatory vaccination policy if the need for it is job-related or if remaining unvaccinated would pose a direct threat to other employees, customers or themselves, according to guidance released last month by the U.S. Equal Employment Opportunity Commission.

For instance, a dentist could make a case that an unvaccinated hygienist would be a danger to others, or a retailer could say a cashier is at risk because of daily exposure to customers.

But there are two main exceptions, said Michelle Strowhiro, employment law partner at McDermott Will & Emery. Employees can object to the vaccine if they think it will exacerbate an established disability or medical condition. They can also turn it down if it goes against their sincerely held religious belief.