Both lawyers and Supreme Court justices acknowledged the "unprecedented" nature of vaccine mandates Friday as the court heard oral arguments in a case that will decide the future of President Biden's COVID-19 OSHA regulations.

"Businesses have encouraged and incentivized their employees to get vaccines," attorney Scott Keller told the Supreme Court Friday. "But a single federal agency tasked with occupational standards cannot commandeer businesses economy-wide into becoming de facto public health agencies. So this court should immediately stay OSHA's unprecedented (emergency temporary standard) before Monday, when OSHA begins enforcement, which is unprecedented."

SUPREME COURT: SOTOMAYOR DENIES BIDEN RULE IS VACCINE MANDATE, DESPITE CLEAR OSHA LANGUAGE

Keller emphasized the unprecedented nature again later on in the arguments, telling Justice Breyer, "We are asking for a stay before enforcement takes effect Monday, and the reason for that is this is an unprecedented agency action."

Breyer dismissed the claim, asking, "How can it conceivably be in the public interest with three quarters of a million people yesterday – goodness knows how many today?"

U.S. Solicitor General Elizabeth Prelogar acknowledged Keller's claims.

"I understand the suggestion here that the standard is unprecedented, but I don't think it would stand scrutiny," Pelogar said. "If you look at the various claims that the applicants are making, they first object to the scope of the standard, the number of employers who are covered. But OSHA commonly issues nationwide standards that govern all employers throughout the nation."

Justice Neil Gorsuch asked Pelogar why OSHA would exercise authority over vaccines now when, in the past, those regulations would be outside the agency's jurisdiction.

"I think it can be explained by the fact that COVID-19 is an unprecedented pandemic that has a magnitude and proportion that OSHA has never seen before," Pelogar said. 

FILE - In this Nov. 5, 2020, file photo the Supreme Court is seen in Washington. (AP Photo/J. Scott Applewhite, File)

In this Nov. 5, 2020, file photo the Supreme Court is seen in Washington. (AP Photo/J. Scott Applewhite, File)

Prelogar used the term "unprecedented pandemic" to refer to COVID-19 repeatedly throughout the oral arguments.

Principal Deputy Solicitor General Brian H. Fletcher backed Prelogar's assertions, claiming OSHA was only acting within the powers and parameters given to it by Congress.

"I think it is not at all unprecedented for the secretary to exercise the same authorities that I was discussing with Justice Thomas here," Fletcher said. "The authorities to set conditions of participation for hospitals and other providers in Medicare and Medicaid to impose very detailed, very prescriptive requirements that would have very high compliance costs."

Eventually, Justice Sonya Sotomayor weighed in and interrupted the oral arguments to say that the regulations were, in fact, something the court had never seen before.

"We've never had a situation like this one before. It's unprecedented," Sotomayor said.

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Sotomayor aggressively pushed back on the term "vaccine mandate" during the Friday hearing.

"There's no requirement here. It's not a vaccine mandate. It's something totally different. And I don't know how much clearer … Congress could have been," Sotomayor said during arguments.