New York City firefighters are calling out sick as a vaccine mandate looms.

More than 2,000 New York City firefighters have taken sick days over the past week in what city officials describe as a large-scale protest against the city’s Covid vaccine mandate for municipal workers, which goes into effect Monday.

“Irresponsible bogus sick leave by some of our members is creating a danger for New Yorkers and their fellow firefighters,” the fire commissioner, Daniel A. Nigro, said in a statement. He attributed the uptick in sick leave to “anger at the vaccine mandate.”

The Fire Department’s deputy commissioner for public information, Frank Dwyer, said that more than 2,000 Fire Department personnel had been out on medical leave at some point over the past week, out of a total uniformed force of about 11,000.

The personnel shortage has put a strain on Fire Department operations. The department said that all its firehouses remain open, but maintaining coverage across the city has required shuffling personnel around to reconstitute fire companies.

The president of the Uniformed Firefighters Association, the union that represents rank-and-file firefighters, said there was no organized sickout. But hundreds of firefighters were feeling the side effects of vaccine doses and were too unwell to work, the U.F.A. president, Andrew Ansbro, said in a phone interview Sunday morning. “Hundreds of guys are feeling flu-like symptoms, because that’s what the shot does to people,” Mr. Ansbro said.

When the city begins enforcing the vaccine mandate on Monday, unvaccinated municipal employees without a medical or religious exemption will be placed on unpaid leave. It’s unclear how the reduction in the city’s work force will affect services ranging from garbage pickup to ambulance wait times.

By Sunday, some 90 percent of municipal workers had gotten at least one shot, leaving just under 23,000 still unvaccinated.

The city reported Sunday that 84 percent of the N.Y.P.D. had gotten at least one dose of the vaccine, up from 70 percent on Oct. 19. Three quarters of firefighters had gotten their first doses by Sunday, officials said.

In the week and a half since Mayor Bill de Blasio announced the mandate, more than 22,000 municipal workers have gotten their first shot and vaccination rates have climbed markedly in many city agencies. Most city agencies now have vaccination rates of 90 percent or above. But a few are notably lower. The Sanitation Department was at 82 percent Sunday. At the Department of Correction, only 63 percent of employees were vaccinated, although correction officers have an extra month to get vaccinated before the mandate goes into effect.

On Sunday, a small number of NYPD employees trickled into headquarters to file retirement papers ahead of the mandate. By 1 p.m., officials counted eight officers who had put in their retirement papers.