Around 12,000 unvaccinated police officers, firefighters, sanitation employees and other municipal workers are still reporting to work this week while New York City evaluates their requests for COVID-19 vaccine exemptions.

The pending exemptions staved off doomsday predictions from the police unions that the city would suddenly be short thousands of officers, though unvaccinated employees still pose a greater risk of spreading the virus to other workers and members of the public.

But this respite could be temporary. Toward the end of the month, threats of a staffing crunch could resurface if the city denies a broad swath of the exemption requests.

The mayor’s office didn’t provide a comprehensive breakdown of how many workers were seeking exemptions at each agency. But multiple officials laid out how the process works, why it is lengthy and why so many unvaccinated workers have been allowed to opt for weekly testing rather than immediately take the shots.

City workers get two chances at an exemption. If their initial paperwork is denied, they can appeal the determination to a city panel or an arbitrator. The city panels are composed of members of the Law Department, Department of Citywide Administrative Services and either the Department of Health and Mental Hygiene or the Human Rights commission, depending on whether the request is a medical or religious exemption. The decisions made on appeal are final, and city officials said they would issue all rulings by November 25th.

NYPD Commissioner Dermot Shea told CNN on Friday that around 6,000 officers had applied for exemptions. In the meantime, the police department had sent fewer than 100 employees home without pay, Shea said. City officials informed WNYC/Gothamist that 1,000 members of the New York City Fire Department (FDNY) and 1,000 Sanitation Department workers were also seeking exemptions. Another 1,000 firefighters and 500 sanitation workers were placed on unpaid leave this week, they said.

Those numbers remain in flux, as the city agreed to extend the application deadline for exemptions through Friday, under pressure from labor unions. The city announced Friday it had reached a deal with 15 labor groups, including unions representing sanitation workers but not ones for police officers or firefighters. According to guidance from the Department of Citywide Administrative Services, all exemptions should be ruled on within seven days of submission.

“Those [requests] are pored over [by] our Office of Employment Discrimination with attorneys reviewing each case individually,” Shea told CNN. “Then they will be either pushed into, ‘Yes the accommodation stands,’” or it’s denied, and there’s an appeal process.”

A city hall official said that after an applicant submits an exemption request, Equal Opportunity Officers in each agency have a conversation with the employee. They rely on guidance from the Centers for Disease Control and Prevention to determine what should be considered a valid medical exemption and whether it should be issued on a temporary or permanent basis.

Currently, the sole contraindication -- a medical reason to avoid a drug -- is severe allergies to just two ingredients found in the shots made by Pfizer, Moderna or Johnson & Johnson. Such allergies are supremely rare, occurring only two to five times for every one million people who take the shots.

This trend makes permanent medical exemptions unlikely. The city will issue temporary medical exemptions if a person has been recently diagnosed with COVID-19 or received a monoclonal antibody therapy or convalescent plasma to fight the virus in the past 90 days. Patients on some immunosuppressive drugs and people with heart inflammation can also earn a temporary pass.

According to the city’s health department, religious exemptions are allowed based on “a sincerely held religious, moral or ethical belief” but not “a request based solely on a personal, political, or philosophical preference.”

Equal Opportunity Officers interview applicants to determine if their belief is sincerely held. Alternatively, the person would have to prove an affiliation with the small set of religions known to oppose the consumption of vaccines. Mayor Bill de Blasio cited Christian Scientists on WNYC’s Brian Lehrer Show in September.

Some people claim they are opposed to any medications -- such as the COVID-19 vaccines -- that use fetal cell lines during their research development process. In those cases, the city asks if they also avoid common drugs like Tylenol or Ibuprofen, according to a city hall official. Those routine meds and others also relied on these fetal cells for development -- often decades after the cells had been originally collected.

A similar process played out when New York City teachers were required to get vaccinated in early October. Overall, 1,200 exemptions were issued but the vast majority were either temporary or permanent medical exemptions. Just 150 people received religious exemptions. As of this week, 96% of the education department’s 161,000-person workforce has taken at least one dose of COVID-19 vaccine.

“People want to know, ‘Do I have an exemption?’ Do I not,” said Martin Scheinman, head of Scheinman Arbitration and Mediation Services. His firm handled thousands of exemption appeals by education department employees, according to city officials. “The arbitrators...worked incredible amounts of hours literally to get this done in a timely fashion so that people would know where they were and that the system would have answers.”

At a news conference on Monday, de Blasio promised strict criteria would be used to evaluate exemptions.

“You'll see a number of people ultimately find that the exemption is not approved, and then they still have that chance to correct [it]. Get vaccinated. Come back [to work],” de Blasio said.