Republicans on Friday vowed to fight U.S. President Joe Biden’s new vaccine mandate covering big companies and federal employees, but business groups that often agree with them on issues like taxes are not joining in.

The, which the White House says would cover 100 million U.S. workers and applies to about two-thirds of all U.S. employees, is being written in part by the U.S. Department of Labor’s Occupational Safety and Health Administration (OSHA).

Nearly three-quarters of eligible Americans have received at least one shot of the vaccine, and opinion polls have found that most support measures like barring the unvaccinated from public spaces and offices.

Within hours of the new measures being announced on Thursday, some lawmakers, state governors and political party officials were threatening lawsuits or pledging to defy it.

“When this decree goes into effect, the (Republican National Committee) will sue the administration to protect Americans and their liberties,” RNC Chair Ronna McDaniel said in a statement.

Reaction from powerful business lobbying groups has been muted. Some large companies have already imposed vaccine mandates of their own, while others have welcomed the move or wondered how they would implement it. More than half of U.S. companies are planning to impose mandates of their own by year-end, according to a recent survey.

The U.S. Chamber of Commerce, which opposes many of Biden’s tax and spending proposals, said it would “carefully review” the vaccination mandate. The Business Roundtable, which represents chief executives, said it welcomed the move. The National Association of Manufacturers, which represents big and small employers, said it would work to make sure the rules don’t hurt business operations.

A majority of those opposed questioned the authority the administration has to mandate vaccines.

“The federal government has no police power, and likewise no authority to force private employers of any size to mandate vaccines,” said the New Civil Liberties Alliance, a nonprofit funded by the Charles Koch Foundation, a deep-pocketed conservative group.

Biden: ‘Have at It”

Asked Friday about possible legal challenges, Biden said “Have at it. I’m so disappointed that particularly some of the Republican governors have been so cavalier with the health of these kids, so cavalier with the health of their communities.”

Several Republican governors said they would resist the administration’s order, though it was not immediately clear how they would do so. “We will fight them to the gates of hell,” South Carolina Governor Henry McMaster said on Twitter.

Florida Governor Ron DeSantis, one of Biden’s most prominent antagonists, also said he would fight the order.

“I do not believe that people should lose their jobs over this issue, and we will fight that,” he said, according to the Orlando Sentinel.

The situation reignites a long-standing U.S. battle over individual rights, states’ constitutional remit to police citizens and regulate public welfare, and the powers of the executive branch.

Similar fights have raged over gun laws and government healthcare. U.S. vaccine mandates in the past have mostly been administered by state and local governments in relation to public venues and schools.

The disease has killed more than 655,000 people in the United States, and deaths and hospitalizations have been rising sharply as the easily transmissible Delta variant of the virus spreads. The vast majority of those are unvaccinated.

Roughly 16% of the adult American population – nearly 34 million people – are currently unvaccinated but open to getting one, according to a recent Reuters/Ipsos poll. The poll arrived at this estimate by asking respondents a series of questions about their vaccination status.

Legal challenges are likely to focus on the executive branch’s power to enforce the requirements. The Cato Institute, a libertarian think tank, said in a blog post that it was unclear whether the administration could act without new legislation from Congress. The Conservative Enterprise Institute, another think tank, said the order would only alienate those who have resisted vaccines to date.

Many Republican lawmakers, who said they have received vaccines and support Americans getting a COVID-19 shot, also accused the administration of overreach.

“Getting the vaccine is a decision to be made in consultation with one’s doctor, not forced on Americans by the government,” said Republican U.S. Senator Ted Cruz.

(Additional reporting by Andy Sullivan, David Shepardson and Andrea Shalal in Washington, Brendan O’Brien in Chicago and Chris Kahn in New York.)