“This is a pandemic in which nearly a million people have died. It is by far the greatest public health danger that this country has faced in the last century,” said Justice Elena Kagan, an appointee of President Barack Obama. “More and more people are dying every day. … There’s nothing else that will perform that function better than incentivizing people strongly to vaccinate themselves.”

But Justice Clarence Thomas questioned whether the current danger from Covid amounted to the kind of crisis that justified the Occupational Safety and Health Administration using an expedited process issuing an “emergency temporary standard” requiring most workplaces with more than 100 workers to enforce a vaccinate-or-mask-and-test mandate.

“The vaccine’s been around quite some time. Covid’s been around even longer,” Thomas, an appointee of President George H.W. Bush, said. “The government could have had notice and comment.”

Among the six Republican-appointed justices, only Chief Justice John Roberts, nominated by President George W. Bush, sounded open to allowing the OSHA rule to take effect. But as the arguments progressed, Roberts seemed more skeptical about the Biden administration’s power to act without specific legislation from Congress. The chief justice said he doubted that the creation of OSHA in 1970 contemplated broad vaccine mandates.

“That was 50 years ago that Congress acted,” Roberts said. “I don’t think it had Covid in mind. That was almost closer to the Spanish flu than to today’s problem.”

However, U.S. Solicitor General Elizabeth Prelogar told the court that the statute authorizing OSHA specifically mentions vaccines and that the need for action is critical.

“We think that there are lives being lost every day,” Prelogar said.

A court spokesperson said Sotomayor, also an Obama appointee, chose to join from her chambers in the Supreme Court building. She has suffered from diabetes since childhood and wore a mask at prior in-person arguments even when other justices did not.

Some of Sotomayor’s early questions Friday were inaudible on the audio feed the court provided for the public to listen in to the arguments. However, the other justices and the lawyers appeared to be able to hear her, and her audio eventually returned.

Ohio Solicitor General Benjamin Flowers was absent from the courtroom after testing positive for coronavirus last month, his office said.

“His symptoms were exceptionally mild and he has since fully recovered. The Court required a PCR test yesterday which detected the virus so for that reason he is arguing remotely,” Bethany McCorkle, a spokesperson for the Ohio attorney general’s office, said via email. She said Flowers is vaccinated and boosted.

Arguing via telehpone, Flowers said the ease of contracting the virus highlights that the OSHA rule doesn’t really address a work-related problem.

“It’s not truly intended to regulate a workplace danger. It’s a danger we all face simply by waking up in the morning,” Flowers said.

Kagan made clear she disagreed.

“Do you know of any workplaces that have not fundamentally transformed themselves in the last two years? … Everybody knows from living their normal lives that every workplace has been affected save for, you know, a few here and there.”

Kagan also noted that workers have less control over contact at work than in other venues. “You have to be there with a bunch of people you don’t know who might be completely irresponsible,” she said.

Lower courts have issued conflicting rulings on the mandates, which cover tens of millions of workers and are central to President Joe Biden’s effort to combat the spread of the virus. The justices will likely rule only on whether the administration can continue to enforce the rules while punting the decision on the underlying regulations — which are being challenged by Republican-led states, businesses and religious groups — back to those courts.

However, the justices’ questions Friday and their ruling could provide hints of the ultimate fate of the vaccine mandates — and of how the administration will approach their implementation as it awaits a final decision.

“It’s going to leave folks with at least a little more clarity as to what the next few weeks might bring,” said attorney Jim Paretti, who represents employers for law firm Littler and is not involved in the cases. But “I’m not optimistic that we will have final answers.”

The broader mandate, from the Department of Labor’s OSHA division, requires employers with 100 or more employees to ensure that their workers are vaccinated or tested weekly and wear masks at work. The other one the court considered, issued by the Department of Health and Human Services, requires employees of health care facilities receiving federal funding to get the jab.

Both requirements, which would affect tens of millions of workers, have been in legal limbo since the Biden administration issued them last year.

The Labor Department mandate was initially blocked by the 5th Circuit Court of Appeals, but the 6th Circuit appeals court lifted the stay after it was chosen via lottery to hear a consolidated version of the various legal challenges to the mandate.

In the health care workers’ case, the Justice Department is asking the Supreme Court to stop two injunctions on the mandate that were issued by the U.S. district courts for the Western District of Louisiana and for the Eastern District of Missouri.

Those challenging the OSHA regulations contend that the agency lacked the legal authority to impose them. They point to, among other things, a 1980 Supreme Court decision that declared OSHA’s ability to issue such emergency temporary standards is “narrowly circumscribed” — which, the challengers say, the vaccine-or-test mandate is not.

“Even in OSHA’s rose-colored view, the Mandate imposes vaccine-or-testing requirements for 84 million Americans … and imposes these requirements on every single industry in the country, amounting to over 264,000 businesses,” Job Creators Network, a business group among those leading the charge against the regulations, said in a filing with the Supreme Court.

The administration counters that OSHA is well within its authority and that lives are at stake if the mandate is blocked.

“OSHA properly determined that [Covid-19] is both a physically harmful agent and a new hazard; that exposure to that potentially deadly virus in the workplace presents a grave danger to unvaccinated employees who are at greatest risk of contracting and spreading the virus at work and suffering serious health consequences as a result; and that the Standard is necessary to protect those employees from the danger of contracting COVID-19 at work,” the administration said in its court filing.

Last month, the Biden administration suspended plans to enforce the vaccine mandate for health care workers, after lower courts froze the measure in two dozen mostly Republican-led states. The administration says that Medicare and Medicaid patients in covered facilities are among the most vulnerable to coronavirus and deserving of protection from their health care providers.

Biden announced the requirement on Sept. 9 as part of a dramatic expansion of the administration’s bid to boost vaccination rates as it redoubled efforts to rein in the virus. Officials anticipated the mandate will affect more than 50,000 health facilities and 17 million workers.

Officials in mostly Republican-led states opposing the requirement argued it was unlawful and would exacerbate health care staffing shortages, particularly in rural areas.

But the administration said in its Supreme Court filing: “It is difficult to imagine a more paradigmatic health and safety condition than a requirement that workers at hospitals, nursing homes, and other medical facilities take the step that most effectively prevents transmission of a deadly virus to vulnerable patients.”

After the 8th Circuit U.S. Court of Appeals turned down the Biden administration’s request that a temporary freeze on the mandate in 10 states be lifted last week, the U.S. Court of Appeals for the 5th Circuit partially lifted a nationwide block on the CMS mandate.

It can now be enforced in about half of the states and is blocked in Alabama, Alaska, Arizona, Arkansas, Georgia, Idaho, Indiana, Iowa, Kansas, Kentucky, Louisiana, Mississippi, Missouri, Montana, Nebraska, North Dakota, Ohio, Oklahoma, South Dakota, Utah, Virginia and Wyoming.

Litigation is also pending in other courts over other Covid-19 vaccination mandates imposed by the Biden administration, including ones for uniformed military personnel, federal workers and federal contractors. Those cases have yet to reach the Supreme Court and are not expected to be the focus of arguments Friday.

Adriel Bettelheim contributed to this report.