Mark Kluger Quoted in New York Times Article: A Court Temporarily blocks Bidenʼs Vaccine Mandate.

A federal appeals panel on Saturday temporarily blocked a new coronavirus vaccine mandate for large businesses, in a sign that the Biden administration may face an uphill battle in its biggest effort yet to combat the virus among the American work force.

The stay, issued by a three-judge panel from the U.S. Court of Appeals for the Fifth Circuit in Louisiana, doesn’t have an immediate impact. The first major deadline in the new rule is Dec. 5, when companies with at least 100 employees must require unvaccinated employees to wear masks indoors. Businesses have until Jan. 4 to mandate Covid vaccinations or start weekly testing of their workers.

But Saturday’s move provided momentum for a wide coalition of opponents of the rule, who have argued that it is unconstitutional. A group of businesses, religious groups, advocacy organizations and several states, including Louisiana and Texas, had filed a petition on Friday with the court, arguing that the administration had overstepped its authority.

It was unclear whether the stay would be a procedural blip for the Biden administration or the first step in the unwinding of the mandate.

At the core of the legal challenge is the question of whether OSHA exceeded its authority in issuing the rule and whether such a mandate would need to be passed by Congress. A similar issue was in play when a Texas court in late 2016 halted an Obama-era Labor Department rule that would have made millions more Americans eligible for overtime pay. The Trump administration, which took office the next year, said it would not defend the overtime rule.

The suit against the mandate stated that President Biden “set the legislative policy” of substantially increasing the number of Americans covered by vaccination requirements, and “then set binding rules enforced with the threat of large fines.”

“That is a quintessential legislative act — and one wholly unrelated to the purpose of OSHA itself, which is protecting workplace safety,” the suit said. “Nowhere in OSHA’s enabling legislation does Congress confer upon it the power to end pandemics.”

A separate lawsuit against the new rule was also filed on Friday in the Court of Appeals for the Eighth Circuit in St. Louis by 11 Republican- led states, among them Texas, Mississippi, South Carolina and Utah.

The Fifth Circuit panel said in a brief order, signed by a deputy clerk, that the judges were blocking the regulation “because the petitions give cause to believe there are grave statutory and constitutional issues with the mandate.” It said the rule was suspended “pending further action by this court.”

The two-page order directed the Biden administration to respond by 5 p.m. Monday to the group’s request for a permanent injunction.

Seema Nanda, the chief legal officer for the Department of Labor, said in a statement that the government was confident in its legal authority to issue the mandate on vaccinations and testing.

“The Occupational Safety and Health Act explicitly gives OSHA the authority to act quickly in an emergency where the agency finds that workers are subjected to a grave danger and a new standard is necessary to protect them,” Ms. Nanda said.

“We are fully prepared to defend this standard in court,” she added.

After both sides have filed briefs, the court will decide whether to lift the temporary injunction, allowing the rule to proceed as planned, or whether to grant a permanent injunction. OSHA could then take the case to the Supreme Court.

“The side that is asking for the injunction has to prove that this rule violates the Constitution,” said Mark F. Kluger, founding partner at the employment law firm Kluger Healey. “That’s a really tough burden to meet,” he added, noting that “federal agencies over the years have become increasingly aggressive about passing or creating rules.”

As an example, he cited the National Labor Relations Board’s rules for union elections. But not all such efforts have been upheld up by the courts.

“The fight is not over and I will never stop resisting this Admin’s unconstitutional overreach!” Attorney General Ken Paxton of Texas, who had challenged the mandate, said in a tweet on Saturday.

Mr. Paxton has previously called the Biden administration’s mandate a “breathtaking abuse of federal power” and is one of the attorneys general who has sued the administration over federal worker vaccine mandates.