NEW YORK (CBSNewYork) — Mayor Bill de Blasio announced what he called a first-in-the-nation vaccine mandate for private companies Monday.

He said the combination of the Omicron variant and holiday gatherings forced him to take “bold” steps. He’s giving businesses just three weeks to make sure their workers are vaccinated.

READ MORE: Ketanji Brown Jackson Joins US Supreme Court

“We in New York City have decided to use a preemptive strike to really do something bold to stop a further growth of COVID and the dangers it’s causing to all of us,” he said in an interview on MSNBC.

WATCH: Mayor De Blasio Announces Vaccine Mandate For Private Companies 

De Blasio said the city will release specific rules on Dec. 15, before the mandate takes effect Dec. 27. He said it will apply to in-person employees, but would not provide any details about enforcement. He also said there will not be a weekly testing option.

“Vaccines work, and vaccine mandates work, particularly when joined with efforts to build vaccine confidence, provide incentives, and improve access, as we have in New York City,” said city Health Commissioner Dr. Dave Chokshi. “We’ve seen this with our health care workers, school staff and public employees. Now it’s time for the private sector to step up and follow suit.”

“Getting the unvaccinated vaccinated is critical to getting our control. We know that that will not happen voluntarily,” Dr. Zeke Emanuel added. “That’s where mandates come in. We know that no one likes to be required to do something, we all like to be given our choice, we are after all Americans, where freedom of choice is essential. But when we have this collective issue that we all have to get vaccinated to protect everyone, we do need to have mandates.”

New York City previously imposed vaccine mandates for city workers, but this will be the first-of-its-kind for the private sector — impacting 184,000 businesses. So far, 94% of municipal employees have gotten their shots.

“This would be my advice to mayors, governors, CEOs all over the country. Use these vaccine mandates,” the de Blasio said. “The more universal they are, the more likely employees will say, ‘OK, it’s time, I’m going to do this,’ because you can’t jump from one industry to another or one company to another. It’s something that needs to be universal to protect all of us.”

Some are raising questions about whether it will slow the return to Manhattan’s Central Business District, which is crucial to the city’s economy.

“In the Bronx, with 15% unemployment, 28% of residents will no longer be able to work on Dec. 27, including 44% of Black young adults, as a result of de Blasio’s vaccine mandate for the private sector,” Staten Island Councilman, the incoming Republican minority leader, Joe Borelli tweeted.

CBS2’s Marcia Kramer asked de Blasio if he thinks the mandate will mean fewer workers will give up telecommuting and return to offices.

READ MORE: Both Sides In Abortion Fight Wait To See How Far DeSantis Will Go In Florida

“I think you’re going to see a lot of people embrace it. You’re going to see a lot of people make the decision it’s time to get vaccinated,” he replied. “I really think we’re going to see this actually help, ultimately.”

The mayor said he spoke with Gov. Kathy Hochul earlier in the morning and briefed Mayor-elect Eric Adams last Friday. The mandate takes effect just days before he leaves office.

“[Eric Adams] has always said he understands right now there are urgent threats facing our city and the mayor’s job is to protect New Yorkers. That’s my responsibility up until the very last minute,” said de Blasio.

“The mayor-elect will evaluate this mandate and other COVID strategies when he is in office and make determinations based on science, efficacy and the advice of health professionals,” Adams told CBS2 in a statement.

Hochul did not respond to CBS2’s request for comment.

New York State Attorney General Letitia James, who is also running for governor, said she supports a “vaccine mandate with a testing option.”

“A mandate alone won’t get us out of crisis, particularly when it’s implemented without input from employees and employers. Science tells us we need everyone to wear masks in public settings; accessible at-home testing; and real health outreach to our communities,” James said in a statement. “This cannot be done municipality to municipality. New York state must finally lead.”

Meanwhile, Borelli is promising to sue to stop the mandate. The Brooklyn Chamber of Commerce said it could mean layoffs this holiday season, and the Partnership for New York City’s Kathryn Wylde told Kramer she wonders if de Blasio is politicizing COVID as he is almost out the door, because he wants to run for governor.

This comes as New York City is also extending the vaccine mandate for indoor dining, fitness and entertainment to include children ages 5 to 11. Starting Dec. 14, kids in that age group will be required to show proof of at least one shot.

Then on Dec. 27, people ages 12 and older will need proof of both doses, except for those who received the Johnson & Johnson vaccine.

Also on Dec. 14, children ages 5 to 11 will have to have at least one shot to participate in “high risk” extracurricular activities.

MORE NEWS: Woman Accused Of Killing Elite Cyclist Is Captured In Costa Rica After 43 Day On The Run

Dr. Chokshi said case rates are currently highest among 5- to 11-year-olds and encouraged parents to get their kids vaccinated.