LITTLE ROCK, Ark. — President Joe Biden’s mandate for many private employers to require their workers to be vaccinated against COVID-19 is facing a wall of opposition from state Republican officials who are passing laws and signing orders to exempt workers, threatening businesses that comply and preparing legal fights over rules that were announced Thursday.

Many Republican officials said they intended to file lawsuits quickly in hopes of halting the mandate, saying the federal government lacks the authority to force vaccines or testing on the private sector.

“This rule is garbage,” South Carolina Attorney General Alan Wilson, a Republican, said Thursday through a spokesperson. “It’s unconstitutional and we will fight it.”

States have been preparing for the requirement since Biden previewed it in September. The Occupational Safety and Health Administration requirements released Thursday call for companies with 100 or more employees to be vaccinated by Jan. 4 or be tested weekly. Failure to comply could result in penalties of nearly $14,000 per violation. Federal officials also left open the possibility of expanding the mandate to smaller employers.

Republican governors or attorneys general in Alabama, Arizona, Arkansas, Florida, Indiana, Iowa, Louisiana, Missouri, Montana and South Dakota said Thursday that they would file lawsuits against the mandate as soon as Friday. The Daily Caller, a conservative media company, filed a challenge in federal court on Thursday.

“While I agree that the vaccine is the tool that will best protect against COVID-19, this federal government approach is unprecedented and will bring about harmful, unintended consequences in the supply chain and the workforce,” Indiana Gov. Eric Holcomb said in a statement.

At a news conference, Florida Gov. Ron DeSantis criticized what he called an “executive fiat” for the private sector. Iowa Gov. Kim Reynolds characterized the mandate as an imposition on personal choice, saying people should be able to make their own health care decisions. She recently signed a bill guaranteeing that people who are fired for refusing a vaccine can qualify for unemployment benefits.

At least 19 Republican-led states have already sued the Biden administration over a separate mandate requiring vaccines for employees who work for federal contractors.

Biden, in a statement Thursday, dismissed the argument from many GOP governors and lawmakers that a mandate for employers will hurt businesses’ ability to keep workers on the job.

“There have been no ‘mass firings’ and worker shortages because of vaccination requirements,” he said. “Despite what some predicted and falsely assert, vaccination requirements have broad public support.”

The administration has been encouraging widespread vaccinations as the quickest way out of the pandemic.

Challenges to the workplace mandate from Republicans and conservative groups are expected to be broad-based and quick, reflecting yet another aspect of the COVID-19 response — from mask requirements to social-distancing guidelines — that has fallen into a partisan divide. Democratic governors and attorneys general were relatively quiet after the OSHA rules were announced on Thursday. From California, Gov. Gavin Newsom issued a simple Twitter message: “The right move.”

All 26 Republican state attorneys general have said they would fight the requirements, and most of them signed a letter to Biden saying as much.

Key to their objection is whether OSHA has the legal authority to require vaccines or virus testing.

In the letter to Biden, the top state government lawyers argued that the agency can regulate only health risks that are specific to jobs — not ones that are in the world generally. Seema Nanda, the top legal official for the U.S. Department of Labor, which includes OSHA, says established legal precedent allows rules that keep workplaces safe and that those rules pre-empt state laws.

That hasn’t stopped state lawmakers and governors for taking a variety of actions aimed at undercutting federal mandates.

Texas Gov. Greg Abbott last month issued an executive order prohibiting private companies or any other entity from requiring vaccines. An Ohio lawmaker has proposed a bill barring schools and colleges from expelling students who refuse vaccines and preventing employers from firing workers who do so.

Arkansas has adopted a law creating a vaccine-mandate exemption for workers who can prove they have COVID-19 antibodies, although a broader measure banning employers from asking about vaccination status failed in the Legislature. The OSHA rule does include a religious exemption, as well as one for people who work exclusively outdoors or away from others — such as from home.

Lawmakers or governors in states including Kansas, South Dakota and Wyoming have called for special legislative sessions to counter vaccine mandates. In Nebraska, not enough state lawmakers agreed to a special session to get one on the calendar, but Gov. Pete Ricketts, a Republican in a GOP-dominated state, has been pushing them to keep trying.

“Right now, there are Nebraskans who are losing their jobs over vaccine mandates,” his office said in a Facebook post Thursday. “Until more Senators step up, these people who are hurting won’t get the help they need.”

In Ohio, factory owner Ross McGregor said he will follow the rules as he would any federal workplace mandate, but not because he agrees with them. McGregor, who said he is vaccinated, is opposed to the new requirement, just as he has publicly opposed efforts by Ohio Republican lawmakers to prevent him from mandating the coronavirus vaccine for his workers.

“At the end of the day, every employer, and every employment situation, dictates what is best,” said McGregor, a former Republican state lawmaker and owner of axle and brake component manufacturer Pentaflex, where he estimates that about half the 115 or so employees are vaccinated. “Having either a ban on mandates or an imposition of mandates goes against that.”