Conservative Supreme Court justices on Friday appeared skeptical that the Biden administration has legal authority to impose a broad coronavirus vaccination-or-testing requirement on large employers, casting doubt on President Biden’s most ambitious plan to fight the pandemic.

But there was a different reaction to the administration’s vaccine mandate for health-care personnel at facilities that receive federal Medicaid and Medicare funds. Some of the justices who expressed doubt about the general workplace requirements seemed more open to the idea that federal officials could require those workers to get vaccinated for the coronavirus.

The answer to both could come quickly — the court is considering emergency petitions either to allow the regulations to go into effect or to stop them, and both sides asked the court to act soon.

It is highly unusual for the justices to hold oral arguments on emergency requests, but Friday’s session went more than three and a half hours. It underscored the national debate over the threat of the coronavirus and the political division over how large a role government can play in requiring its citizens to be vaccinated.

There was a real-time dynamic as well. Besides the impending deadlines, some justices came armed with the latest numbers on the surging omicron variant, and their very actions displayed their concern.

All of the justices have been vaccinated and received boosters, but for the first time since they resumed in-person arguments, all began Friday’s session masked, with the exception of Justice Neil M. Gorsuch. His seatmate, Justice Sonia Sotomayor, 67 and diagnosed with diabetes as a child, participated remotely from her chambers.

On Jan. 13, the Supreme Court blocked the Biden administration from enforcing a vaccination-or-testing requirement for large employers. Here’s what to know. (Julie Yoon/The Washington Post)

In weighing previous challenges to coronavirus restrictions and requirements, the court has been largely deferential to states — but skeptical of the powers of federal agencies. That seemed to be the case when the court considered the rule proposed by the Occupational Safety and Health Administration (OSHA), which would cover about 80 million workers.

A majority of justices seemed inclined to agree with private businesses and 27 Republican-led states challenging the order that OSHA’s proposed action was beyond a federal agency’s powers.

Such a workplace requirement “sounds like the sort of thing that states will be responding to or should be, and that Congress should be responding to … rather than agency by agency, the federal government, the executive branch acting alone,” said Chief Justice John G. Roberts Jr.

Washington lawyer Scott A. Keller, representing the National Federation of Independent Business, said it was an unprecedented imposition by the federal government on private workplaces.

“Our nation’s businesses have distributed and administered hundreds of millions of covid vaccines to Americans. Businesses have encouraged and incentivized their employees to get vaccines,” Keller told the court. “But a single federal agency tasked with occupational standards cannot commandeer businesses economywide into becoming de facto public health agencies.”

Gorsuch seemed to agree with Roberts. Justices Clarence Thomas and Samuel A. Alito Jr. asked questions even more skeptical. Justice Amy Coney Barrett wondered if the regulation was drawn too broadly or should be more targeted at specific industries and workplaces, rather than imposed on all businesses with 100 or more employees.

The court’s three liberal justices seemed confident the federal agencies had proper authority in both cases and exasperated by the questioning.

Several times, Justice Stephen G. Breyer mentioned that there were “nearly three-quarters of a million people, new cases” every day.

“I would find it, you know, unbelievable that it could be in the public interest to suddenly stop these vaccinations,” Breyer said.

“More and more people are dying every day. More and more people are getting sick every day,” said Justice Elena Kagan. “This is the policy that is most geared to stopping all this.”

Keller said state officials and private businesses can and have acted to protect workers, but that the federal government’s policy would impose new costs and cause a “massive economic shift” by leading employees to quit.

Sotomayor pointed out that “catching covid keeps people out of the workplace for extraordinary periods of time.”

Ohio Solicitor General Benjamin M. Flowers, who made his argument by phone because he tested positive for coronavirus in advance of the hearing, said the Biden administration’s policy was too sweeping in scope and “not truly intended to regulate a workplace danger. It’s a danger that we all face simply as a matter of waking up in the morning.” He noted that vaccinations cannot be undone.

But Solicitor General Elizabeth B. Prelogar, representing the Biden administration, said the policy is at the heart of the federal government’s responsibility.

“Exposure to covid-19 on the job is the biggest threat to workers in OSHA’s history,” Prelogar said. “The court should reject the argument that the agency is powerless to address that grave danger.”

The hearing took place in a building that has been closed to the public for nearly two years because of the pandemic. Only court staff, lawyers in the cases, credentialed reporters and the justices’ law clerks are allowed to attend oral arguments, and all must be masked and possess negative coronavirus test results.

Technically, the court is not deciding the legality of the administration’s initiatives, only whether they may be implemented while lawsuits challenging them continue.

But the questioning focused on the merits of the cases and whether federal agencies have proper authority to impose rules that could boost the nation’s vaccination rate, which is almost 65 percent.

The other challenged policy is a Centers for Medicare and Medicaid Services vaccination requirement for what the White House says is more than 17 million health-care workers at 76,000 facilities that receive federal money tied to those programs.

The administration points to federal law that gives the secretary of the Department of Health and Human Services the ability to impose requirements necessary for the “health and safety” of patients.

For decades, it says, the secretary has had authority to require participating health-care providers to establish programs for the prevention and control of infectious diseases within the facilities.

In court Friday, Brian H. Fletcher, the administration’s principal deputy solicitor general, said many health-care workers already are required to be vaccinated against hepatitis, measles and the flu and that the medical community overwhelmingly supports the policy.

“I think it would be bizarre to say that the secretary’s authority to protect the health and safety of Medicare and Medicaid patients does not include the authority to adopt a measure that you see other regulators adopting, the medical community urging and other providers adopting voluntarily,” Fletcher said.

Roberts and Justice Brett M. Kavanaugh seemed more receptive to the argument that the administration has sway over those workers and facilities.

Roberts noted the close connection between coronavirus and the risk to elderly and low-income patients treated at facilities that receive federal funds.

“People already get sick when they go to the hospital, but if they go and face covid-19 concerns, well, that’s much worse,” Roberts said.

Kavanaugh wondered why the states were bringing the challenge if the rule would be such an imposition on facilities and their workers.

“Where are the regulated parties complaining about the regulation?” he asked.

Missouri Deputy Attorney General Jesus A. Osete said the regulations would make dedicated health-care workers “choose between losing their jobs and complying with the government’s vaccine mandate.”

He said it would create an “imminent crisis” in rural areas where objecting workers cannot be easily replaced.

Louisiana solicitor general Elizabeth Murrill, also forced to make her arguments remotely because of the court’s testing requirement, said the rules would “force millions of people working for or with a Medicare or Medicaid provider to undergo invasive, irrevocable, forced medical treatment.”

Kagan was unmoved. All the government is saying with the vaccination requirement, she said, is “the one thing you can’t do is to kill your patients. So you have to get vaccinated so that you’re not transmitting the disease that can kill elderly Medicare patients, that can kill sick Medicaid patients.”

But Gorsuch was wary of the government conditioning funds on the vaccine requirement. “Could it mean, should it mean, have we in other cases interpreted similar language to mean, you can’t use money in a way that commandeers a state or private entity?” he asked.

A panel of the U.S. Court of Appeals for the 11th Circuit dismissed a request from Florida to stop the requirement. But a district judge in Missouri stopped the rules, and the 5th Circuit agreed with a challenge from Louisiana.

In the workplace regulation, federal law grants OSHA authority to issue emergency rules for up to six months to protect employees “exposed to grave danger” from “substances or agents determined to be toxic or physically harmful or from new hazards.” The administration contends that gives OSHA not only the authority but also the responsibility to act.

The temporary rule would give companies with 100 or more workers a choice: mandate all employees be vaccinated or require unvaccinated employees to provide weekly negative coronavirus test results and wear face coverings to work on-site.

The rules were set to take effect Jan. 4, but OSHA pushed back the date in response to the litigation and said it would not immediately issue citations for those not in compliance.

Soon after the administration announced the rules for private companies in November, the U.S. Court of Appeals for the 5th Circuit blocked enforcement of the policy.

But lawsuits emerged around the nation and were consolidated for review by a different court. A panel of the U.S. Court of Appeals for the 6th Circuit dissolved the 5th Circuit’s stay, saying the rules could go into effect.

Because of the uncertainty surrounding the litigation, OSHA announced that it would not penalize companies for not complying with employee testing requirements before Feb. 9, as long as employers show “reasonable, good faith efforts” to meet the standards.

In response to concerns about a shortage of health-care workers, Fletcher told the court that the HHS secretary has given facilities some flexibility to meet the new requirements, including an additional 60 days to get employees fully vaccinated. The agency also will hold off on any enforcement action, Fletcher said, as long as 90 percent of the workforce is vaccinated and the facility has a plan to immunize its remaining workers.

The OSHA cases are National Federation of Independent Business v. Department of Labor and Ohio v. Department of Labor. The health-care worker cases are Biden v. Missouri and Becerra v. Louisiana.