The Supreme Court heard oral arguments Friday to determine the fate of the White Houses federal vaccine rules for workers , pressing the Biden administration and GOP state officials on the question of whether federal agencies can require COVID-19 vaccination or testing in the workplace.

The justices are expected to decide relatively quickly whether to block the Biden administration from imposing the vaccine rules while litigation plays out in lower courts. Rulings against the White House would be a significant setback for the presidents vaccination campaign at a time when COVID-19 caseloads have ballooned due to the omicron variant.

If the justices allow either or both rules to stand, it could nudge more workers into getting vaccinated in order to keep their jobs.

The court holds a 6-3 conservative majority, and has already upheld the ability of states to implement vaccine requirements for workers during the pandemic. But the line of questioning Friday suggested the conservative justices were skeptical of the federal governments power to impose broad vaccine regulations.

One rule , issued through the Occupational Safety and Health Administration, would require employers with at least 100 workers to implement programs in which those workers either show proof of vaccination or undergo weekly testing for the coronavirus. The White House estimates that it would cover 84 million employees at work sites around the country.

The other rule , issued through the Centers for Medicare and Medicaid Services, would require workers at health care facilities that receive Medicare or Medicaid funding to be vaccinated. That regulation would impact some 17 million employees at 76,000 workplaces, including hospitals, long-term facilities and dialysis centers, the administration has said.

The two regulations prompted a thicket of lawsuits filed by Republican state officials and business groups who argued the White House overstepped its legal authority. Citing the broad economic effects of such rules, the plaintiffs argued that neither OSHA nor CMS could issue them without an act of Congress.

Scott Keller, who argued against the OSHA rule on behalf of a business lobby, the National Federation of Independent Business, said the regulation would lead to permanent worker displacement as workers left jobs due to the vaccine-or-test requirement.

A single federal agency tasked with occupational standards cannot commandeer businesses economywide into becoming de facto public health agencies, Keller said.

Justice Elena Kagan was skeptical that OSHA overstepped its bounds. She asked Keller how the COVID-19 pandemic wouldnt qualify as an emergency worthy of OSHAs intervention, calling it by far the greatest public health danger this country has faced in the last century.

This is the policy thats most geared toward stopping all of this, she said. Theres nothing else that will perform that function better than incentivizing people strongly to vaccinate themselves. Why isnt this necessary and grave?

She acknowledged the rule was an extraordinary use of emergency power, but called the pandemic an extraordinary circumstance.