(NewsNation Now) — The Biden administration’s COVID-19 vaccine-or-test requirement for large employers may not survive the conservative-leaning Supreme Court, according to one legal expert.

The court heard arguments Friday on a challenge to the mandate, which applies to businesses with at least 100 employees. Conservative justices on the court appeared to view the administration’s requirement as overstepping government authority.

Brian Dean Abramson, an adjunct professor of vaccine law at Florida International University’s College of Law, said on “NewsNation Prime” on Sunday that the mandate could be stopped or at least altered by the court.

“Certainly I think it is unlikely to go into effect exactly as it stands,” Abramson said.

Abramson added he thinks it’s possible the court stays the rule or at least adds conditions to make it difficult for OSHA to prosecute companies that are not complying.

Fully vaccinated and mostly masked, 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 seemed more open to a separate vaccine mandate for most health care workers.

Abramson said Justice Amy Coney Barrett highlighted a potential weakness of the mandate in that OSHA’s rule didn’t take into account the particular circumstances of companies or employees.

“That’s kind of a real infirmity of this regulation, as it has been put out,” Abramson said. “It’s clear that it was put out under some pressure from the Biden administration to get something done very quickly.”

Abramson added this is the first time the federal government has attempted to broadly require vaccinations among such a large portion of the population, beyond just requiring them for smaller groups, such as members of the military or immigrants.

The Occupational Safety and Health Administration rule is supposed to take effect Monday, although the agency has said it would not impose fines on businesses that don’t comply before late February. Abramson said the requirement for unvaccinated workers at large companies to be tested weekly doesn’t start until Feb. 9, so consequences for noncompliance would not start immediately.

Abramson also said a second mandate that would apply to virtually all health care staff in the country appears to be more palatable to the conservative justices.

The rule 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 Associated Press and NewsNation’s Joe Khalil contributed to this report.