WASHINGTON (AP) — Hoping to set a model for employers nationwide, President Joe Biden will announce Thursday that millions of federal workers must show proof they’ve received a coronavirus vaccine or submit to regular testing and stringent social distancing, masking and travel restrictions.

An individual familiar with the president's plans, who spoke on condition of anonymity to confirm details that had yet to be announced publicly, emphasized that the new guidance is not a vaccine mandate for federal employees and that those who decide not to get vaccinated aren’t at risk of being fired.

The new policy amounts to a recognition by the Biden administration that the government — the nation’s biggest employer — must do more to boost sluggish vaccination rates, as coronavirus cases and hospitalizations rebound, driven largely by the spread of the more infectious delta variant.

Biden has placed the blame for the resurgence of the virus squarely on the shoulders of those who aren't vaccinated.

“The pandemic we have now is a pandemic of the unvaccinated,” Biden said during a visit Wednesday to a truck plant in Pennsylvania, where he urged the unvaccinated to “please, please, please, please” get a shot. A day earlier, he mused that “if those other 100 million people got vaccinated, we’d be in a very different world.”

The administration on Wednesday was still reviewing details of the expected guidance, and significant questions about its implementation and scope remained. It was unclear whether the president would issue similar requirements for the military and how federal contractors would be affected. The administration is announcing the move now with the hope that it will give agencies enough time to craft their own guidelines and plans for implementation before workers return fully to the office.

The announcement is expected to come as part of broader remarks Thursday that Biden promised would outline “the next steps in our effort to get more Americans vaccinated.”

The individual said the conversation around the new vaccine guidance had been in the works for some time and was intended to provide an example for private companies to follow as they get ready for workers to return this fall. But it’s just the latest policy shift from the administration during a week of new coronavirus mitigation efforts, as the White House grapples with a surge in coronavirus cases and hospitalizations nationwide driven by the delta variant and breakthrough infections among vaccinated Americans.

On Monday, the Department of Veterans Affairs became the first federal agency to require vaccinations, for its health workers. And on Tuesday, the Centers for Disease Control and Prevention reversed its masking guidelines and said that all Americans living in areas with substantial or high coronavirus transmission rates should wear masks indoors, regardless of their vaccination status.

With the latest CDC data showing that Washington, D.C., is facing substantial rates of transmission, by Wednesday reporters and staff were again masking up at the White House.

The new guidance on vaccinations for federal employees reflects the reality that Biden’s national vaccination drive has fallen short of his goals. Public opinion seems to have hardened around the vaccines, with a recent poll from The Associated Press-NORC Center for Public Affairs Research finding that among American adults who have not yet received a vaccine, 35% say they probably will not, and 45% say they definitely will not.

"Doing more of the same just will not work,” said Dr. Leana Wen, a former Baltimore health commissioner who’s become a leading public health commentator on the pandemic.

“This is the logical next step,” Wen continued. “If you want to be going in to work and interacting with other people, then you have to be sure you wouldn’t have COVID, and you can do that either by getting vaccinated or by testing.”

About 60% of American adults have been fully vaccinated. Biden missed his goal of having 70% of adults get at least one shot by July 4. The latest figure is 69.3%.

Federal workers and contractor employees are dispersed throughout the nation, including many in states where vaccine skepticism runs high. New York University public service professor Paul Light suggested the new guidance from the Biden administration could help boost vaccination rates in states where there's been significant resistance.

“You can’t throw a stick without hitting a fed in many parts of the country,” he said.

Light noted that the government’s influence goes well beyond the people it directly employs. Federal contractors and grant recipients will have to weigh how they’ll adjust to vaccination requirements from Washington.

“If the federal government were to say that everybody who works for the government directly or indirectly must be vaccinated, that’s a massive footprint,” Light said.

He estimated that the federal government directly employs 2.2 million full-time civil servants, plus 1.4 million active-duty military personnel and about 500,000 workers in the U.S. Postal Service. Private contractor employees working on federal jobs number about 5 million, and there are 1.8 million other people employed under federal grants.

While the administration hopes the new guidance will boost vaccination rates, having Biden wade squarely into the middle of the ongoing political debate surrounding vaccines could backfire if it further fuels GOP criticism and distrust of the vaccine among the president's detractors.

The AP-NORC poll found that views on vaccinations divide sharply along party lines, with Republicans far more likely than Democrats to say they have not been vaccinated and definitely or probably won’t be, 43% to 10%.

Indeed, South Carolina GOP Rep. Ralph Norman, who has resisted the new mask requirements on Capitol Hill, hinted at the fight to come over the new guidelines.

“To require individuals to provide proof of vaccination would be a massive intrusion on the doctor-patient relationship and the privacy of the individual,” he said in a statement.

The Biden administration may also have to grapple with legal challenges to the latest guidelines.

The federal workplace is governed by layers of rules and regulations, so private employers as well as state and local governments will be looking at the White House vaccination policy to signal how far they can go without triggering resistance from employees or even lawsuits.

But while the Justice Department and the federal Equal Employment Opportunity Commission have both said no federal laws prevent businesses from requiring vaccinations as a condition of employment, litigation is certain to follow workplace mandates, said Sharon Perley Masling, an employment lawyer who leads the COVID-19 task force at Morgan Lewis.

“It’s a really challenging issue for employers,” Masling said. “We have seen employers explore a whole range of options, from encouraging vaccinations, to incentivizing vaccinations, to mandating vaccinations for new hires, or for everyone.”

Among examples from major companies, Delta Air Lines and United Airlines are requiring new employees to show proof of vaccination. Goldman Sachs is requiring its employees to disclose their vaccination status but is not mandating they be vaccinated.

If an employer does set a hard requirement, employees can ask for an exemption for medical or religious reasons under federal civil rights laws.

According to EEOC rules, the employer must provide “reasonable accommodation that does not pose an undue hardship on the operation of the employer’s business.” Some accommodations could include masking up at work, social distancing, working a modified shift, regular COVID-19 testing or the option to work remotely, or even offering a reassignment.