Vaccine passports haven’t taken off. Lawsuits have been filed over mandatory requirements to get the shot. Rising concerns over the Delta variant of COVID-19 have employers on edge and with the potential to threaten reopening plans, as cases rise in the U.S. after already battering Europe and India. 

One big hurdle? The amount of people who choose not to get a vaccine. While the majority of the U.S. has gotten at least one dose, more than 30% of adults still have not, according to CDC data. A survey of 1,000 Americans conducted by the Society for Human Resource Management reveals that 28% of employees said they wouldn’t get a COVID-19 vaccine—even if it cost them their job. 

There are several reasons one might decline to get vaccinated: health reasons, age, religion, or politics. But the sheer number of unvaccinated individuals in the U.S. poses risk for exposure in offices—and as of now, there’s no clear way for how companies should appropriately respond.

Employers are anxious to get employees back into the office and back to work. Nearly half of 1,500 small business owners surveyed by Digital.com said that most of their job functions required in-person attendance, and 40% of them said that they would fire employees who wouldn’t return to the office full-time.

How companies handle opening back up varies by industry or job-type. Companies that have had large majorities of their staff working remote throughout the duration of the pandemic may have an easier time than travel companies, which are under heightened risk of exposure as well as scrutiny, incentivizing them to take a tougher approach. 

On Wall Street, it’s been a mixed bag. Goldman Sachs has required its employees to report their vaccination status. Bank of America, BlackRock and Morgan Stanley are only allowing vaccinated employees back in the office.

“Starting July 12 all employees, contingent workforce, clients and visitors will be required to attest to being fully vaccinated to access Morgan Stanley buildings in New York City and Westchester,” said a memo from Morgan Stanley’s chief human resources officer that was obtained by the Financial Times last month.

Charles Schwab doesn’t have a specific policy regarding vaccines, according to a spokeswoman.

So far, such vaccine mandates at work are relatively rare. Only 10% of Fortune 500 CEOs say they plan to require vaccinations, according to Fortune data, although 31% are still considering the policy.

On the other hand, many employees wish their employers would require it. Some 45% of U.S. adults say workplaces should require employees to show proof that they received a COVID-19 vaccine in order to return to the office, according to a Fortune and SurveyMonkey poll of more than 2,000 adults—53% say they shouldn’t.

There could be multiple reasons employers are hesitant to require vaccinations. For one, fear of being sued—particularly after 117 unvaccinated employees filed a lawsuit against their employer, Houston Methodist Hospital, over its vaccine mandate, even though it was dismissed in court. And even if companies mandate vaccination, they are required to make accommodations for those with medical conditions or those who don’t want to be vaccinated for religious reasons, said Kimberly McNeil, a Society for Human Resource Management HR Knowledge Advisor, who has been fielding questions from the organization’s members. On top of all that, some companies worry about losing employees in the midst of labor shortages.

For now, many companies and organizations are turning to an incentive-based approach to encourage employees to get their shot—from T-shirts, bonuses and paid time off. After all, T-shirts are a lot cheaper than a lawsuit.