WASHINGTON (AP) — The Supreme Court began hearing arguments Friday on major Biden administration work rules to bump up the nation’s vaccination rate against COVID-19 at a time of spiking coronavirus cases because of the omicron variant.

The justices were taking up the questions of whether to allow the administration to enforce a vaccine-or-testing requirement that applies to large employers and a separate vaccine mandate for most health care workers. The arguments were expected to last at least two hours.

Early in the arguments, some members of the court’s conservative majority expressed skepticism for the employer rule. Justice Neil Gorsuch and Chief Justice John Roberts suggested officials had overstepped. Roberts said it’s “hard to argue” that officials had been given the power to act by Congress. Justice Amy Coney Barrett suggested that a problem with the rule was its broad scope.

But 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 it 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.

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.

The challengers argue that the vaccine rules exceed the administration’s authority, but Solicitor General Elizabeth Prelogar, the administration’s top Supreme Court lawyer, wrote that both are needed to avoid unnecessary hospitalizations and deaths.

Keeping the vaccine mandate for health care workers on hold “will likely result in hundreds or thousands of deaths and serious illnesses from COVID-19 that could otherwise be prevented,” Prelogar wrote.

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.