Biden announces plan to mandate vaccines at businesses with 100 or more workers.

President Biden said on Thursday that the Department of Labor is preparing to mandate that all businesses with 100 or more workers require their employees to either get vaccinated against the coronavirus or face mandatory weekly testing.

The effort marks the government’s biggest push yet to draw employers into a campaign to vaccinate the country and would affect some 80 million workers.

The Occupational Safety and Health Administration is drafting an emergency temporary standard to implement the requirement, according to the White House.

“Some of the biggest companies are already requiring this — United Airlines, Disney, Tyson Foods, and even Fox News,” Mr. Biden said during a speech Thursday.

Mr. Biden also said the Department of Labor will require the businesses to offer their employees paid time off to get vaccinated.

The Biden administration also intends to require vaccination for federal workers and contractors, as well as for 17 million health care workers in hospitals and other institutions that receive Medicare and Medicaid funding.

Mr. Biden pleaded for more businesses to help the effort to increase vaccinations. “To those of you running large entertainment venues — from sports arenas, to concert venues, to movie theaters — please require folks to get vaccinated or show a negative test as a condition of entry,” he said.

OSHA, which is part of the Department of Labor, oversees workplace safety, which it will likely contend extends to vaccine mandates. The agency has issued other guidelines for pandemic precautions, such as a rule in June requiring health care employers to provide protective equipment, provide adequate ventilation and ensure social distancing, among other measures.

“I think that the Department of Labor probably is in good stead to be able to justify its mandate for health and safety reasons for the workers,” said Steve Bell, a partner at law firm Dorsey & Whitney specializing in labor and employment.

“They’ve got a broad pretty solid basis for saying: ‘We’re here to protect the workers, and this is part of our purview, and we think that this is something that will protect employees,’” he said.

Still, OSHA’s authority does not mean it won’t face pushback or lawsuits challenging the order, particularly as some states move to curb vaccine mandates through executive orders or legislation. And enforcement may be a challenge, since there is no national system for employers to track or report vaccination status.

A number of large employers, ranging from CVS Health to Goldman Sachs to Chevron, have already put in place some form of vaccine mandate. Companies have been eager to get their workers back into the office and return to a degree of normalcy.

Still, many of these mandates are not comprehensive. Companies like Walmart and Citigroup have mandates for their corporate employees, but not for frontline workers in stores or at branches. Many companies are dealing with labor shortages and varying levels of vaccine hesitancy among workers.

For those companies, the ability to mandate testing in lieu of vaccination may prove significant. Firms like AstraZeneca and JPMorgan Chase already require vaccines or weekly testing and are therefore in compliance with the expected order.

Still, testing is a financial burden for employers. It also requires ongoing administration, with the potential to miss infections. And experts say testing must be accompanied by other measures, like social distancing.

Mr. Biden has raised the pressure on private employers to help with vaccination efforts. In August, the White House met with executives of companies that had mandated vaccination, including Scott Kirby of United Airlines, to discuss how they could encourage fellow business leaders to do the same.

After the Food and Drug Administration granted full approval to Pfizer-BioNTech’s coronavirus vaccine on Aug. 23, Mr. Biden encouraged corporate vaccine mandates.

“If you’re a business leader, a nonprofit leader, a state or local leader, who has been waiting for full F.D.A. approval to require vaccinations, I call on you now to do that,” he said at the time. “Require it.”

Katie Rogers contributed reporting.