The Biden administration on Thursday set Jan 4 as the deadline for medium and large businesses with 100 or more employees to have all workers fully vaccinated against COVID-19 or face weekly tests. The mandate will affect about 84 million workers in private sector.

The emergency order was issued by the Occupational Safety and Health Administration (OSHA) at the Labor Department. It isn't clear how many of those employees affected by the order are unvaccinated.

OSHA left open the possibility of expanding the requirement to smaller businesses. It asked for public comment on whether employers with fewer than 100 employees could handle vaccination or testing programs.

The regulations will make companies require that unvaccinated workers test negative for COVID-19 at least once a week and wear a mask while in the workplace.

The Biden administration also requires workers at healthcare facilities that receive Medicare or Medicaid funding to be vaccinated by Jan 4 without the option of being tested weekly. That will affect an estimated 17 million healthcare workers.

The pandemic has killed more than 750,000 Americans so far. The global toll has surpassed 5 million.

OSHA said companies that fail to comply with the regulations could face penalties of nearly $14,000 per violation. Unvaccinated workers are also required to wear masks at their workplace. Workers can ask for exemptions on medical or religious grounds. People who work outdoors or at home are exempt from the vaccination mandate.

The federal government didn't require the employers to pay for the weekly test of unvaccinated workers. This will put some economic pressure on employees to get vaccinated.

The rules were released after weeks of regulatory review and meetings with business groups, labor unions and others.

"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," President Joe Biden said Thursday in a statement. "Together, these rules will cover about 100 million Americans — two-thirds of all workers in America.''

The Centers for Disease Control and Prevention data cited by OSHA indicate that, as of Oct 18, 68.5 percent of people age 18 years or older are fully vaccinated, leaving approximately 31.7 million unvaccinated or not fully vaccinated.

OSHA said that vaccine mandates imposed by state governments and large employers have been effective in increasing vaccination rates. It cited that the vaccination rate in Tyson Foods' workforce went from 45 percent to 91 percent in less than two months after a mandate. Similarly, United Airlines achieved 97 percent vaccination rate within a week of the deadline.

By OSHA's estimate, the vaccine mandate will prevent more than 6,500 unvaccinated workers from dying of COVID-19 over the next six months, and an additional 250,000 currently unvaccinated workers will avoid being hospitalized during that same time period.

The National Retail Federation, an industry trade group including some major retail chains, issued a statement stating that the vaccine mandate would "impose burdensome new requirements on retailers during the crucial holiday shopping season".

The federal mandate is likely to lead to more lawsuits along political lines.

Senate Republicans have said they would try to repeal it using a law known as the Congressional Review Act. Some GOP governors including those in Florida, Indiana, Georgia, Nebraska and Iowa already have said they plan to challenge the mandate.

Republican Texas Governor Greg Abbott issued an executive order last month banning any entity from requiring a vaccine mandate. While the federal order will void part of the ban, Abbott's order will still apply to local governments, school districts and smaller businesses.