The Supreme Court’s conservative majority appeared skeptical Friday of the Biden administration’s authority to impose a vaccine-or-testing requirement on the nation’s large employers. The court also heard arguments on a separate vaccine mandate for most health care workers.

But the COVID circumstances did not appear to outweigh the views of the court’s six conservatives that the administration overstepped its authority in its vaccine-or-testing requirement for businesses with at least 100 employees.

“This is something the federal government has never done before,” Chief Justice John Roberts said, casting doubt on the administration’s argument that a half-century-old law, the Occupational Safety and Health Act, confers such broad authority.

Roberts and Justices Brett Kavanaugh and Amy Coney Barrett probably hold the key to the outcome in both cases, as they have been more receptive to state-level vaccine requirements than the other three conservative justices. Barrett and Kavanaugh also had tough questions for Solicitor General Elizabeth Prelogar, the administration’s top Supreme Court lawyer.

The court’s three liberal justices suggested support for the employer rule. Justice Elena Kagan said officials have shown “quite clearly that no other policy will prevent sickness and death to anywhere like the degree that this one will.” And Justice Stephen Breyer said he found it “unbelievable” that it could be in the “public interest” to put that rule on hold. He said that on Thursday there were some 750,000 new cases in the country and that hospitals are full.

"We have hospitals that are almost at full capacity with people severely ill, on ventilators," said liberal =leaning Justice Sonia Sotomayor. "Tell me what's irrational about rules of that nature when it is the workplace that puts you into contact with people that will put you at risk."

Beginning Monday, unvaccinated employees in big companies are supposed to wear masks at work, unless the court blocks enforcement. Testing requirements and potential fines for employers don’t kick in until February.

Legal challenges to the policies from Republican-led states and business groups are in their early stages, but the outcome at the high court probably will determine the fate of vaccine requirements affecting more than 80 million people.

"I think effectively what is at stake is whether these mandates are going to go into effect at all," said Sean Marotta, a Washington lawyer whose clients include the American Hospital Association. The trade group is not involved in the Supreme Court cases.

Administration lawyer Prelogar told the justices that COVID-19 “is the deadliest pandemic in American history and it poses a unique workplace danger.” OSHA has estimated that its emergency regulation will save 6,500 lives and prevent 250,000 hospitalizations over six months.

Nearly 207 million Americans, 62.3% of the population, are fully vaccinated, and more than a third of those have received a booster shot, including the nine justices.

Andy Slavitt, a former adviser to the Biden administration on COVID-19, said the vaccine requirements are extremely effective for 15% to 20% of Americans "who don't like to get a shot, but they will and don't have any strenuous objection."

The high court will be weighing in on administration vaccine policies for the first time, although the justices have turned away pleas to block state-level mandates.

But a conservative majority concerned about federal overreach did bring an end to the federal moratorium on evictions put in place because of the pandemic.

Both vaccine rules would exacerbate labor shortages and be costly to businesses, lawyer Scott Keller argued Friday on behalf of more than two dozen business groups. Without an immediate order from the court, “workers will quit right away,” Keller said.

The second regulation at issue is a vaccine mandate that would apply to virtually all health care staff in the country. It covers health care providers that receive federal Medicare or Medicaid funding, potentially affecting 76,000 health care facilities as well as home health care providers. The rule has medical and religious exemptions.

Decisions by federal appeals courts in New Orleans and St. Louis have blocked the mandate in about half the states. The administration has said it is taking steps to enforce it in the rest.

Both cases came to the court on an emergency basis, and the court took the unusual step of scheduling arguments rather than just ruling on briefs submitted by the parties. Unlike in other cases the court hears, a decision from the justices could come in weeks if not days.

Because of the pandemic the justices heard the cases in a courtroom closed to the public. Only the justices, lawyers involved in the cases, court staff and journalists were allowed inside. The public could listen live, however, a change made earlier in the pandemic when the justices for nearly 19 months heard cases via telephone.

The court has been asking arguing lawyers to have negative coronavirus tests and participate remotely if they have positive tests. Ohio Solicitor General Benjamin Flowers, who was arguing against the employer rule, had tested positive for COVID-19 after Christmas, had mild symptoms and fully recovered, but a test on Sunday required by the court detected the virus, a spokeswoman said. He had been vaccinated and had a booster shot.

Louisiana Solicitor General Elizabeth Murrill who was arguing against the health care workers rule, was also arguing remotely “based upon the court’s protocol,” state Attorney General Jeff Landry said. Landry was at the court for Friday’s arguments.

It is the first time since the court returned to in-person arguments in October that lawyers were arguing remotely.