Indiana Gov. Eric Holcomb said he's directing the state's labor department to "work with the Attorney General on a lawsuit challenging the federal government" in the wake of the Biden administration's announcement that large businesses must begin enforcing a vaccine-or-test mandate Jan. 4.

Holcomb in a statement Thursday called Biden's plan "an overreach of the government’s role."

"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," he said.

Nebraska Gov. Pete Ricketts also said he'd "fight" the mandate.

"If this rule is allowed to take effect, many Nebraskans will be at risk of losing their jobs over something that should remain a personal health choice," Ricketts said in a statement. "I have been in communication with the Attorney General today, who will be taking the lead on Nebraska’s legal review of the potentially illegal federal vaccine mandate. We will fight back."

The vaccine mandates for businesses with 100 or more workers is a part of a sweeping new federal plan that identifies COVID-19 as an occupational hazard in the workplace. Industry groups had pressed the administration to give businesses extra time, warning that imposing any mandates now would exacerbate the nation’s worker shortage. The plan gives federal contractors an extra month to comply, sliding back the previously-set Dec. 8 deadline.

As Dr. Anthony Fauci and CDC director Rochelle Walensky testified Thursday before the Senate Health, Education, Labor, and Pensions Committee, they spoke to the vaccine mandate that'll soon be in effect for businesses with 100 or more employees.

Walensky said, "We know the most disruptive thing in our workforce is to have a COVID outbreak and to have workers in that workforce come down with COVID infection, severe disease, and in some cases, death."

"Vaccination, as we've seen, decreases your risk of infection by sixfold, decreases your risk of hospitalization and death by tenfold -- even during this delta surge. So there's absolutely a public health priority to get people vaccinated and to continue the important prevention and mitigation strategies including masking to keep them safe," she said.

-ABC News' Cheyenne Haslett

New York City kids ages 5 to 11 can get $100 for getting vaccinated at a city-run site, Mayor Bill de Blasio announced.

The United Kingdom has authorized Merck's COVID-19 treatment, becoming the first country in the world to do so.

Clinical studies suggest Merck's COVID-19 pill, molnupiravir, may reduce the ability of the virus to multiply in the body, thereby preventing hospitalization or death in patients with mild to moderate COVID-19.

The UK's Medicines + Healthcare products Regulatory Agency said the antiviral drug was found to be safe and effective following a stringent review of the available evidence.

-ABC News' Christine Theodorou