Officials say it's happening in all five boroughs. A manpower shortage that has caused the temporary shutdown of at least 10 fire companies because a number of firefighters have called-out sick.
Department officials are accusing the unions tonight of staging an illegal job action.
They are allegations union leaders vehemently denied.
"Is there a sickout? Not to my knowledge, no," said Andrew Ansbro with the Uniformed Firefighters Association.
"We don't condone any job action, nor do we inform anybody to do a job action," said Jim McCarthy, president of the Uniformed Fire Officers Association.
"I have had members that have received the vaccination say they are having flu like symptoms and they've had to go sick," Ansbro said. "The department is allowing people to have a couple days off after they get the vaccination."
Commissioner Daniel A. Nigro released the following statement:
"The excessive sick leave by a group of our Firefighters because of their anger at the vaccine mandate for all city employees is unacceptable, contrary to their oaths to serve, and may endanger the lives of New Yorkers. Despite these actions by some, the Department will continue to respond to all calls for help that come our way."
Meanwhile, State Sen. Zellnor Myrie was on the receiving end of a protest Friday staged by four firefighters in uniform, on duty, in a fire truck with lights on, from ladder 113 in Brooklyn.
"It is incredibly disturbing, that those entrusted with keeping us safe, would be on duty, protesting a vaccine mandate that had nothing to do with what a state elected official has jurisdiction over my staff is rattled, they're shaken up by it," Myrie said. "And frankly, I am upset that we're even having this conversation."
The senator was not there at the time but a person familiar with the conversation tells ABC News the firefighters spoke to a staff member and said they said they wanted to let the community know that the trucks weren't going to be running and that they were going to shut down firehouses.
The person says it was a "cordial conversation" though at one point the firefighters said the "city would have blood on its hands."
But firefighters from ladder 113 were responding to calls Friday night. The four firefighters have been relieved of duty and will face disciplinary action.
Fire protection in New York remained in doubt as the deadline approached. Thousands have protested this week-determined to defy the city's vaccination mandate.
The mandate said that all municipal employees must have been vaccinated against COVID-19 by 5 p.m. Friday. So far 77% of FDNY members are vaccinated.
Mayor Bill de Blasio insisted that contingency plans will be adequate.
"Because the fire department has been through situations already, including last spring when a huge number of members were out," de Blasio said. "They had to make a lot of adjustments. And they did it very effectively."
As for the NYPD, department commanders believe their crisis may be averted.
They say a vaccination rush by hundreds of officers over the past 36 hours will allow the department to police the city with no significant impact on public safety.
"I think we're heading in the right direction, obviously," said Commissioner Dermot Shea. "We have a very growing population of vaccinated members of the NYPD."
The vaccine hesitancy among so many has left city commissioners frustrated -- Shea among them.
"This time last year, we were fighting like heck to get vaccines for our members to keep them safe," Shea said. "And now we have them, and we're having a debate."
The department vaccination rate is now at 84%, and after the department administered more than 1,000 vaccinations Friday.
Meanwhile, the sanitation department's vaccination rate went up 9% on Friday. However 24% of the department remains unvaccinated.
ALSO READ | FDNY unions protest vaccine mandate outside Gracie Mansion on Upper East Side
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