New York City is bracing for a tense week ahead as a COVID-19 vaccine mandate for municipal workers went into effect on Monday.

Mayor Bill de Blasio said 9 in 10 municipal workers in the city have gotten at least one COVID-19 vaccine. He tweeted late on Saturday that 91 percent of city workers had received at least one shot, compared with 83 percent as of Friday.

Under the city mandate, those who have not received at least one vaccine dose will be put on unpaid leave starting from Monday, raising the possibility of shortages of police, fire and emergency medical services. The city has more than 300,000 employees.

The New York Police Department, or NYPD, which employs approximately 36,000 officers and 19,000 civilian employees, reported an 84 percent vaccination rate as of Sunday morning. The Fire Department of New York, or FDNY, said on Sunday afternoon that 80 percent of its employees were vaccinated－75 percent of firefighters, 87 percent of emergency medical technicians and 90 percent of civilian employees.

More than 24,000 city workers, including police officers and firefighters, will be forced to stay home on Monday when the mayor's vaccine mandate goes into effect, reported the New York Post. That includes more than 8,000 police officers, 3,700 FDNY employees and nearly 2,000 sanitation workers.

Staffing shortages forced the department to close 26 fire companies in all five boroughs on Saturday, reported the Post, adding that one insider said hundreds of firefighters angered over the mandate were using medical leave to stay home.

"As of 7:30 this morning, 26 FDNY stations, including five in my district, have closed due to Mayor de Blasio's decision to lock unvaccinated firefighters out of work," said Nicole Malliotakis, a US representative and Staten Island Republican, on Saturday.

Fire Commissioner Daniel Nigro denied reports that some firehouses had closed.

Creating danger

"The department has not closed any firehouses," said Nigro in a statement on Sunday. "Irresponsible bogus sick leave by some of our members is creating a danger for New Yorkers and their fellow firefighters. They need to return to work or risk the consequences of their actions."

Andrew Ansbro, FDNY Firefighters Association president, told WABC Radio that he does not have any knowledge of a "sickout".

"I have had members that have received the vaccination say they are having flu-like symptoms, and they've had to go sick. The department is allowing people to have a couple days off after they get the vaccination."

The FDNY confirmed late on Sunday that 2,000 firefighters were on medical leave, NBC reported.

De Blasio said Sanitation Department crews will now have 12-hour shifts, as opposed to the usual eight hours, and start working on Sundays to ensure that garbage does not pile up.

The mandate has also become an issue in Tuesday's mayoral election.

Democratic mayoral front-runner Eric Adams has not said whether he would maintain the vaccine mandate if elected.