A federal appeals court suspended the Biden administration’s new vaccine requirement for private companies, delivering a major blow for one of the White House’s signature attempts to increase the number of vaccinations to corral the pandemic.

The decision was issued by a panel of three judges appointed by Republican presidents in the U.S. Court of Appeals for the Fifth Circuit. The judges wrote that there was “cause to believe there are grave statutory and constitutional issues with the mandate,” staying the order while the court assesses it in more depth.

The ruling came in response to a lawsuit filed Friday by a group of plaintiffs including Louisiana Attorney General Jeff Landry (R), part of a wave of lawsuits against the order from mostly Republican-aligned groups and politicians.

Landry on Saturday called it a “major win for the liberty of job creators and their employees.”

“The Court’s action not only halts Biden from moving forward,” he said, calling the requirement unlawful, “but also commands the judicious review we sought.”

The unsigned, four-paragraph order from the panel temporarily stops Biden’s mandate but is not a ruling on the merits of the policy. The court gave the Justice Department until 5 p.m. Monday to respond to the challenger’s request for a more permanent halt to the mandate.

The Department of Labor instituted the ruling through the Occupational Safety and Health Administration.

“The U.S. Department of Labor is confident in its legal authority to issue the emergency temporary standard on vaccination 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,” said Seema Nanda, the solicitor of labor.

The vaccine requirement, released by the Biden administration on Thursday after weeks of anticipation, ordered companies of 100 or more employees to institute mandatory vaccinations for their staff or weekly testing, with a Jan. 4 deadline.

President Biden on Sept. 16 said coronavirus vaccines will help with the economic recovery and save lives. (The Washington Post)

Federal officials spent weeks hammering out the policy, aware of the high number of legal challenges it would face, but believing that the order was well within the Department of Labor’s powers to keep workplaces free of “grave dangers” in times of emergency.

The requirement is supported by a majority of the American public according to public opinion surveys and is a critical step to increasing vaccination rates and getting the pandemic under more firm control, according to public health experts.

But it has generated intense opposition from the small but vocal factions of the country that have organized against pandemic measures, like masking, business restrictions and mandatory vaccinations. Governors and attorneys general in mostly Republican-controlled states have vowed to fight it vigorously in court; 11 joined a separate lawsuit filed against it on Friday in federal court in Missouri. Two companies in the Midwest, represented by a conservative advocacy group, have also filed suit against the rule.

Many conservatives believe the requirement is a fundamental overstep of federal authority.

Vaccination requirements from state and local governments and private companies have largely held up in court so far, but the Biden administration’s federal mandate is more broad than these measures.

Because of the testing option the order gives employers, it is not a true vaccine mandate, and is softer than many of the requirements instituted by private companies. Workers who choose not to be vaccinated at companies that allow testing are required to wear masks under the rule, as well. Overall, it does not apply to employees who work remotely, outside or otherwise don’t report to workplaces where other people work or shop.

Mandates appear to have helped drive an increase in vaccinations. United Airlines, which had one of the strictest mandates for a major air carrier, said its employee vaccination rate increased to more than 99 percent. Delta, which used financial penalties and testing requirements, saw the employee vaccination rate jump to 90 percent from 75 percent. Tyson Foods said recently that at least 96 percent of its employees were vaccinated in advance of its Nov. 1 deadline — up from under 50 percent before it announced the mandate in August.

Many hospitals in New York saw vaccination rates increase to more than 95 percent by the deadline of the state’s mandate for health-care workers, up from the 70 percent to 80 percent range before the rule was announced. In California, major hospitals saw vaccination rates increase to about 90 percent after a similar, albeit slightly less stringent, mandate.

The ruling was signed by Judges Edith Jones, a Ronald Reagan appointee; and Kyle Duncan and Kurt Engelhardt, both appointed by Donald Trump. The New Orleans-based 5th Circuit is considered one of the country’s most conservative appeals courts.

Ann E. Marimow contributed to this report