• The American Medical Association, in a filing with U.S. Court of Appeals for the Sixth Circuit, said Covid-19 poses a "grave danger to the public."
• The AMA, arguing in support of Biden's policy, told the court that transmission of Covid in the workplace has played a major role in spreading the virus.
• "The more workers who get vaccinated, the closer we are to slowing the spread of the virus and creating a safer environment," the doctors' association told the court.

The largest group of doctors in the U.S. has warned a federal appeals court that halting President Joe Biden's vaccine and testing requirements for private businesses would "severely and irreparably harm the public interest" as the highly transmissible delta strain of Covid-19 spreads.

The American Medical Association, in a filing with the U.S. Court of Appeals for the Sixth Circuit, said Covid-19 poses a "grave danger to the public" that has "wreaked havoc in communities across the country," killing more than 755,000 Americans, hospitalizing 3.25 million people, and infecting more than 46 million.

"COVID-19 presents a severe risk to public health in this Circuit and throughout the nation," the doctors' association said in the filing. "As of November 12, 2021, over 76,000 people have died from COVID-19 in the four states in this Circuit alone," the group said. The Sixth Circuit covers Kentucky, Michigan, Ohio and Tennessee.

The AMA, arguing in support of Biden's policy, told the court that transmission of Covid in the workplace has played a major role in spreading the virus, pointing to outbreaks in industries ranging from meat-processing and transportation to hospitality and construction.

The doctors' association said Covid vaccines are safe and highly effective, and provide the most effective way to protect workers from infection. The AMA argued that vaccine requirements are "critical" to curb or eradicate infectious diseases, citing past vaccine mandates for measles and smallpox.

"The more workers who get vaccinated, the closer we are to slowing the spread of the virus and creating a safer environment," the doctors' association told the court. The AMA filed as a friend of the court to provide its expertise, saying it has "an interest in providing evidence-based guidance on public health issues."

"Immediate, widespread vaccination against COVID-19 is the surest way to protect the U.S. workforce and the public and to end this costly pandemic," the group said.

The AMA's filing comes as a coalition representing doctors, nurses and pharmacists issued a joint statement supporting Biden's policy. The group included the AMA, the American College of Physicians, the American Academy of Pediatrics, the American College of Emergency Physicians, the National League for Nursing, the National Medical Association and the American Public Health Association among others.

"We—physicians, nurses and advanced practice clinicians, health experts, and health care professional societies—fully support the requirement that workers at companies with over 100 workers be vaccinated or tested," the groups said in a statement published last Thursday. "We encourage all businesses with 100 or more employees to not delay in implementing this standard," they said.

The U.S. Court of Appeals for the Fifth Circuit has forced the Biden administration to suspend implementation and enforcement of the requirements. The appellate court, one of the most conservative in the country, halted the requirements pending review on Nov. 6. Judge Kurt D. Engelhardt, in an opinion for a three-judge panel on Nov. 12, said the requirements are "fatally flawed" and "staggeringly overbroad," raising "serious constitutional concerns."

The Biden administration has said the court-ordered pause "would likely cost dozens or even hundreds of lives per day" as the virus spreads.

Public health officials are worried that the U.S faces another wave of infection as Americans head indoors to escape the winter cold and gather with families over the holidays. The U.S. is recording more than 92,000 infections on average per day, up 16% from last week, according to data from Johns Hopkins University.

Roughly 50,000 Americans are currently hospitalized with the virus, up 6% from a week ago, based on a seven-day average of Department of Health and Human Services data. The daily average of 1,122 reported fatalities tracked by Hopkins is down slightly, by 3%, over the past week. But rising case count indicates that the death rate could spike in the next few weeks.

More than two dozen lawsuits have been filed against the vaccination and testing requirements. Republican attorneys general, private companies, and national industry groups such as the National Retail Federation, American Trucking Associations and the National Federation of Independent Business have sued to overturn the requirements. Labor unions have sued to have the requirements expanded to cover smaller businesses and protect more workers.

Those lawsuits were transferred to the Sixth Circuit last week after the Biden administration asked a multidistrict litigation panel to consolidated them in a single court through random selection. The Sixth Circuit has a majority of Republican-appointed judges.

The AMA originally filed the brief last week. The brief was entered into the case's consolidated docket on Monday.

The Occupational Safety and Health Administration, which polices workplace safety for the Labor Department, issued the rules under its emergency authority established by Congress. OSHA can shortcut the normal rulemaking process, which can take years, if the Labor secretary determines a new workplace safety standard is necessary to protect workers from a grave danger.

Businesses with 100 or more employees had until Jan. 4 to ensure their workers were vaccinated or submitted a negative Covid test weekly to enter the workplace. Unvaccinated employees were required to start wearing facemasks indoors at the workplace starting Dec. 5.

The AMA argued that the requirements are "appropriately structured to strongly encourage vaccination."

With the requirements currently on pause as the litigation plays out, the future of Biden's policy is uncertain. Legal experts believe the case will ultimately be decided by the Supreme Court.

"Whoever loses in the Sixth Circuit is going to the Supreme Court,"  Carl Tobias, a professor of law at the University of Richmond, told CNBC last week.

Clarification: The American Medical Association originally filed its brief on Nov. 15. The brief was filed into the consolidated case's docket on Monday, Nov. 22.