The White House affirmed Tuesday that the Biden administration has no intention of requiring Americans to carry documentation to prove their COVID-19 vaccination status.

"The government is not now nor will we be supporting a system that requires Americans to carry a credential," White House press secretary Jen Psaki on Tuesday. "There will be no federal vaccinations database, and no federal mandate requiring everyone to obtain a single vaccination credential."

Psaki acknowledged that private parties and non-profit organizations had been considering such tools, though made it clear that a federal mandate was not on the table due to concerns over privacy.

Such credentials, known as "vaccine passports," could be complicated to carry out in the U.S. because of privacy, equality, and practical concerns. The notion of a vaccine passport has already faced resistance in Texas, with Gov. Greg Abbott issuing an order Monday barring some businesses from mandating proof of vaccination.

As the White House and Texas push back against vaccine passports, countries around the globe are requiring varying levels of proof of vaccination for their citizens. The European Union and China committed to moving ahead with government-mandated "vaccine passports" for citizens to prove they’ve been inoculated against COVID-19.

The EU has plans for a “digital green pass” for EU citizens, and UK Prime Minister Boris Johnson said Monday the country would test out vaccine passports. China’s government also said it intended to develop a certification program for citizens to show proof of vaccination or negative test results. And in February, Israel initiated its “Green Badge” system to exclude non-vaccinated individuals from certain activities.

'Extraordinarily difficult' in the U.S.

Legal experts say the U.S. government could pull off a successful and legal certification scheme. However, data privacy and anti-discrimination hurdles, as well as technical ones, could make a federal vaccine passport system tough to impose on Americans.

“It would be extraordinarily difficult in the U.S.,” Georgetown Law professor Lawrence O. Gostin previously said about the government adopting a certification system aimed at restraining Americans’ liberties absent proof of COVID-19 vaccination.

“How can we assure this information is held private, and it won’t be given out to police, employers, immigration, or other places?” Gostin asked.

And with a vaccine passport system, he added, enormous privileges automatically extend to privileged populations that often have greater access to vaccines, opening the door to potential discrimination claims.

“Do we really want to give already very privileged people more privilege, while the poor and racial minorities are left behind? Racial minorities have been vaccinated at much lower rates, and they're also distrustful of vaccines, and so it puts them at a disadvantage,” Gostin said.

Experts who Yahoo Finance spoke with last month agree that one of the most robust U.S. laws protecting health information, the Health Insurance Portability and Accountability Act, known as HIPAA, would not prevent the U.S. government from mandating a vaccine credentialing program.

"The reason HIPAA's not relevant is because it applies to doctors, hospitals, health insurers, basically," Kirk J. Nahra, a data privacy lawyer and partner with WilmerHale, told Yahoo Finance in March. "And for an employer, the only way to be relevant is if they learned that somebody had tested positive because they submitted an insurance claim to the employee health benefits program."

'They could easily wipe away any federal challenges to privacy'

Technically, there may be no legal barrier preventing U.S. governments from adopting a vaccine passport requirement, but Harvard Law School professor and health law policy expert Glenn Cohen previously told Yahoo Finance that he too, thinks it unlikely.

“It’s hard to think that would violate any existing law,” Cohen said. Even so, he said Congress could use legislation to supersede potentially contravening federal laws, including HIPAA, the Americans with Disabilities Act (ADA), or the Genetic Information Nondiscrimination Act (GINA).

“As long as Congress was clear enough about it, they could easily wipe away any federal challenges to privacy,” Cohen said. “And that’s true with other laws.”

The government has a lot of flexibility when enacting laws to protect the public health, Nahra said. Privacy concerns would most likely arise based on how the government uses the health data it collects, how it stores and transmits the information, and who can access it, he said.

As for discrimination concerns, he said, governments would need a strong enough justification concerning the public health condition to back up excluding unvaccinated Americans from particular places or activities. If a court were ruling on whether exclusions were legal, he said, it would likely turn on the extent of the exclusion.

“Okay, you don't have [the vaccine]? Therefore what?” Nahra asked to illustrate the point. “If the answer is you can't leave your house, there's going to be various constitutional challenges. If you can't go on public transportation, maybe that's more legitimate.”

On March 26, New York Governor Andrew Cuomo rolled out a pilot certification program developed in partnership with IBM (IBM) called the “Excelsior Pass." The pass allows mobile phone users to upload recent COVID-19 negative test results, or vaccine status in exchange for a mobile or printable QR code. While the state has not mandated the pass, the system could test legal boundaries.

According to Cuomo, the pass is intended to help major stadium venues comply with a mandate to ensure that staff and spectators receive a negative COVID-19 PCR test within 72 hours of an event. The system has been tested at Barclays Center and Madison Square Garden.

'It's not just between me and the airline'

Private entities, on the other hand, may have broader flexibility to refuse service to the unvaccinated.

Already, employers and businesses are requiring workers and customers to submit to temperature checks and health questionnaires, and offering workers perks in exchange for getting vaccinated. Some businesses are now mulling whether to require that employees become vaccinated before returning to work.

Still, the experts said, laws and guidance covering employer-employee relationships do little to sort out the duties that private businesses — such as retail stores, airlines, hotels, sports and concert venues — owe to the broader public.

“What we're learning with COVID, is that it’s not just between me and the airline,” Nahra said. “There are a whole bunch of other people that have an interest in my information, as well, right? All the other passengers."

A more likely potential roadblock, absent Congress' override, Cohen said, is the ADA, which requires employers to accommodate workers who can't get vaccines due to health concerns, and Title VII of the Civil Rights Act that protects employees who refuse vaccines over religious objections. The ADA also prohibits certain businesses generally open to the public — such as restaurants, movie theaters, schools, day cares, recreation facilities, and doctors' offices — from discriminating based on disability.

So how do private businesses weigh the risk of shutting their doors and services to those who either can't or won't get vaccinated? And how much information about a customer's vaccination or COVID-19 test history can they share with other customers?

"Our laws don’t deal with that...There’s a gap in the law,” Nahra said.

An earlier version of this story was published on March 5, 2021.

Alexis Keenan is a legal reporter for Yahoo Finance and former litigation attorney.

Follow Alexis Keenan on Twitter @alexiskweed.