Supreme Court Justice Sonya Sotomayor aggressively pushed back on the term "vaccine mandate" during a Friday hearing on the Biden administration's contested COVID-19 regulations outlined by the Occupational Safety and Health Administration (OSHA).

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

SUPREME COURT HEARS ORAL ARGUMENTS ON BIDEN VACCINE MANDATES: LIVE UPDATES

This appears to be tapping into a claim that, because the mandate allows for mandatory vaccinations to be substituted by weekly testing, it is therefore not a mandate.

OSHA has said it is part of its Vaccination and Testing Emergency Temporary Standard (ETS), which covers employers with 100 or more employees.

"The ETS requires covered employers to establish, implement, and enforce a written mandatory COVID-19 vaccination policy with an exception for employers that instead establish, implement, and enforce a written policy that requires unvaccinated employees to undergo weekly COVID-19 testing and wear a face covering at the workplace instead of vaccination."

Scott Keller, representing the National Federation of Independent Business, argued that the OSHA regulations had originally been passed to protect workers from unvaccinated coworkers, and were now obsolete due to "CDC guidance contradicting foundational assumptions" of the regulations.

Sotomayor quickly snapped back, saying, "Yes, that may be true, but we are now having deaths at an unpressed amount, catching COVID keeps people out of the workplace for extraordinary periods of time."

The SCOTUS justice went on to compare safety regulations protecting from workplace hazards to mandates countering human illness with mandated treatment.

"And there have been proof and certain industries like the medical industry that when vaccines are mandated – and there's no mandate here for a vaccine – there is a masking mandate no different than there is when we tell people that if there are sparks flying in the workplace where you have workers have to be provided, will have to wear a mask."

"So that's no different in my mind than this," she added.

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Upholding a stay on President Biden's workplace vaccine mandate, a federal appeals court ruled in November that White House chief of staff Ron Klain’s retweet of an MSNBC journalist's Twitter post was an endorsement of her claim about a mandate "work-around," according to a report. 

On Sept. 9, Klain retweeted MSNBC anchor Stephanie Ruhle’s post that said, "OSHA doing this vaxx mandate as an emergency workplace safety rule is an ultimate work-around for the Federal govt to require vaccinations." 

The Fifth Circuit Court of Appeals mentioned the retweet in its decision reaffirming its stay on Biden's mandate following a legal challenge from Texas and several other states, according to a Reuters reporter. 

Fox News's Adam Shaw contributed to this report.