Millions of Americans have chosen not to get a coronavirus vaccine. But with the shots readily available and virus cases ticking back up in parts of the country, a growing number of employers, universities and businesses are now issuing some form of a vaccine requirement.

Under many of these orders, those who remain unvaccinated, including people who can't get a vaccine because of a disability or conflicting religious beliefs, will instead have to follow strict guidelines like regular COVID testing, masking and social distancing.

"I think probably what these companies are thinking — for those individuals — requiring them to be masked, or constantly tested, is a reasonable accommodation," Joel Friedman, a law professor at Tulane University, said. "And that's probably correct."

Another component of the shifting landscape on vaccines is their expected full approval by the Food and Drug Administration. The vaccines are currently administered under an emergency use authorization, so full approval could alleviate concerns over their safety — and encourage even more organizations to make them a requirement.

Here's a look at who could ask you to get the vaccine:

Can your employer require you to get the vaccine?

The short answer is yes, though a vast majority have not.

Any company is within its legal rights to require employees get vaccinated, barring any conflicting disability or religious belief, according to the U.S. Equal Employment Opportunity Commission.

Walmart, the nation's largest private employer, is requiring that a good chunk of its workers — an estimated 1.6 million, including those at its headquarters — receive a vaccine.

The Walt Disney Co., Google, Facebook, Tyson Foods and Uber are some of the other large companies requiring at least some of their employees to be vaccinated.

State governments and the Biden administration have also issued vaccine mandates in their capacity as employers, but not in a way that affects the general public.

As many as 7 million federal workers are now required to show proof of vaccination, under new guidelines announced by President Joe Biden in late July. If they do not, they'll have to follow strict rules on mandatory masking, weekly testing and social distancing. The military said it would follow suit with its employees.

States like North Carolina, New York and California are also requiring their state employees do the same. And mandatory vaccination orders are also popping up for workers in state hospital systems across the country. This includes most hospitals in Massachusetts, some in South Carolina and others in North Carolina.

And these requirements aren't a HIPAA violation, either — while the act protects a patient's confidential health information, including what one's health care provider can share with others, it doesn't cover what employers can ask for.

What about your college or university?

Yes. And they may have already done so if you attend one of the more than 500 colleges and universities — including the university system in states like California, Illinois, Colorado and New York — that are making the vaccine an enrollment requirement if students want to take classes in-person this coming semester.

While some campuses are asking students to provide a proof of vaccination, others are incentivizing students with exemptions from mask mandates.

But that doesn't mean everyone is happy. A federal judge upheld Indiana University's vaccine requirement last month after a group of students filed a lawsuit. The mandate is also a challenge for international students who may not have access to one of the eight WHO-approved vaccines.

What about children in K-12 schools?

That can depend on whether the child is in a public or private school. While children ages 12 to 17 are now eligible for the vaccine, and it's likely that younger children will become eligible this fall, it's not a requirement for attending a public K-12 school anywhere in the country.

Private schools, along with day care centers and camps, can decide whether to require their students to get a vaccine or not.

Most children already receive routine vaccinations for other diseases, like tetanus, polio and chickenpox, to fulfill school enrollment requirements. So a state-level requirement for a COVID vaccine in the future is a possibility.

Could your local or state government require you to get the vaccine? What about the federal government?

Local and state governments can enforce a vaccination because of a legal precedent set by the 1905 Supreme Court ruling in Jacobson v. Massachusetts, which let states require their residents get smallpox vaccinations.

New York City will this month begin requiring proof of vaccination for dining inside restaurants, entering fitness centers and taking part in other indoor activities.

At the same time, some states, like Florida, are using their authority to enforce the opposite, and have banned agencies and businesses from requiring proof of vaccination.

And as for the federal government, that's a no. The director of the CDC, Dr. Rochelle Walensky, confirmed in July that there would be no nationwide mandate.

What if you want to travel internationally?

It depends. While certain countries remain closed to Americans, those that welcome travelers require either proof of vaccination, or a recent negative COVID test. So long as you can provide the latter, a vaccination usually isn't required.

What about other businesses where you're just a customer?

It depends on where you live.

A handful of restaurants in major cities like Philadelphia and Los Angeles now require customers show proof of a vaccination. A couple of restaurants and bars in Kansas City are also doing the same. Only some of these places will let customers present a recent negative COVID test instead.

Similar policies are showing up in gyms. Equinox and SoulCycle will require their customers and staff in New York City provide proof of vaccination next month before extending the same requirements to other locations.

How do the religious exemptions work?

While employers have a legal responsibility to reasonably accommodate an employee's religious beliefs, and universities can allow religious, and even philosophical, exemptions for the vaccines, restaurants and other businesses don't have that same duty toward customers, according to Elizabeth Sepper, a law professor at the University of Texas at Austin.

What exactly constitutes a religious belief is open to interpretation, she said, from the teachings of the major organized religions to less traditional religious beliefs.

One religious argument people have made against vaccines, according to Sepper, is that they undercut their faith in God's ability to protect their bodies from harm. Others are opposed to vaccines that were developed or tested using cells derived from the fetal tissue of elective abortions that took place decades ago.

But employers are also protected from being burdened — they only have to provide a realistic alternative to the employee, usually in the form of frequent testing, mask mandates or social distancing.

"The obligation to the employer is to be reasonable," Sepper said. "Not to roll over backward, and let an employee do whatever they want."

And the number of people who could successfully petition for a religious exemption from a vaccine mandate is probably small.

"If we saw religious exemptions in any large number, I would doubt their sincerity," Sepper said. "Because there's no major religion that opposes vaccination."

Will more organizations require a vaccine in the future?

It's likely. Friedman, who anticipates that more businesses will require vaccinations in the future, maintains that the legal precedent for mandating vaccines is already there, it's just up to these entities to decide to act on it.

"It's not a legal decision," he said. "It's a political and economic judgment that these companies are making."

This article originally appeared in The New York Times.