President Joe Biden's administration on Thursday set a January 4 deadline for enforcement of strict rules intended to push tens of millions of American workers into getting Covid-19 vaccines.

The mandates targeting businesses with more than 100 employees, as well as health care workers and federal contractors, represent the most aggressive steps Washington has taken against the virus and its Delta variant, which has hobbled economic recovery.

"Vaccination is the single best pathway out of this pandemic. And while I would have much preferred that requirements not become necessary, too many people remain unvaccinated for us to get out of this pandemic for good," Biden said in a statement.

"I'm calling on employers to act. Businesses have more power than ever before to accelerate our path out of this pandemic, save lives, and protect our economic recovery."

Under the regulations, workers at private firms will have to receive their second shot by January 4, 2022, or wear a mask in the workplace and undergo weekly testing.

Employers will be required to provide paid time off for workers to get vaccinated.

The rules will require the majority of American health care workers to receive vaccines, while regulations for federal contractors will depend on their workplace, the White House said.

The regulations will affect more than two-thirds of the country's workforce, according to the Biden administration, and join mandates announced by major employers in the country as well as some states.

Biden debuted the mandates in September amid growing concern over the country's flagging vaccination rate, leaving federal agencies to finalize their implementation.

The Republican opposition has decried them as an overreach and some business groups warn they would be disruptive.

'Turning point'

The world's largest Covid-19 outbreak is among issues that have weighed down Biden's presidency in recent months.

His Democratic party suffered a humiliating defeat in Virginia's governorship election this week, while lawmakers in Congress have yet to reach an agreement on two spending bills Biden has put at the center of his policies.

Economic growth soared and millions went back to work after Biden took office in January just as Covid-19 vaccines became widely available.

But third-quarter growth slumped and September's hiring was the weakest of the year as the Delta wave sent infections soaring and made businesses cautious.

The president on Tuesday hailed a Food and Drug Administration decision to allow children aged 5-11 to receive the Pfizer-BioNTech vaccine as a "turning point."

Convincing reluctant adults to get widely available and free vaccines is another matter.

While some businesses including major air carriers have imposed their own vaccine requirements, Republican lawmakers compare the mandate to a "dictatorship," and state attorney generals from the party have already sued over the rules.

States versus Washington

The governor of Texas went as far as to put a ban on Covid-19 vaccine mandates, including private companies.

The White House said the "new rules preempt any inconsistent state or local laws, including laws that ban or limit an employer's authority to require vaccination, masks, or testing."

Solicitor of Labor Seema Nanda meanwhile said the government "will consider whether to extend the rule to smaller companies."

Workers who choose not to follow the regulations will not be exempt from disciplinary action by their company, Deputy Assistant Secretary of Labor for Occupational Safety and Health Jim Fredrick said, adding that his agency could assess penalties of up to $136,000 against rule-breakers.

Industry reacted with unease to the requirements, with the Society for Human Resource Management releasing a poll last month saying 90 percent of employers surveyed would find it difficult to implement the mandate.

They asked the government to seek public comment before rolling out the regulations.

David French, of the National Retail Federation, warned "the Biden administration has chosen to declare an 'emergency' and impose burdensome new requirements on retailers during the crucial holiday shopping season."