BOSTON (AP) — Boston's vaccination mandate won't go into effect on Monday for some city workers, following a judge's order Thursday.

A Massachusetts Appeals Court judge issued a temporary stay on the mandate for unionized firefighters and certain unionized police officers challenging it. The judge ruled the vaccine mandate will be paused pending a review of a lower court order.

Earlier this week, the city firefighters union and two police officers' unions appealed a state Superior Court ruling denying a request to temporarily halt the measure while the court weighed the unions' broader challenge.

The Boston Police Superior Officers Federation, one of the union involved in the suit, called on Boston Mayor Michelle Wu to also hold off applying the mandate to unionized teachers and patrol officers.

The union said the order means the city will not be able to enforce the mandate against firefighters, police supervisors or detectives until the unions' appeal has been decided.

“Over the past few months, Mayor Wu has undermined collective bargaining and the labor rights of so many city workers," the union said in a statement. “This has never been an anti-vaccine issue. Mayor Wu ignored written agreements and refused to meet with unions in good faith.”

Wu responded that 95% of city workers have already been vaccinated against the virus.

“Vaccination is our most powerful tool in this ongoing public health emergency, and we look forward to filing our response with the court,” she said in an emailed statement.

Labor unions have clashed in public and in the courts with Wu on the mandate, even as most city workers have already met its requirement to receive at least one dose of a COVID-19 vaccine by Sunday, or face being placed on unpaid leave.

The firefighters union wants the city to provide an option to submit to weekly COVID-19 testing instead of being vaccinated. The city’s largest police union has also opposed the mandate, and the city teachers’ union has voiced concerns the mandate will disproportionately hurt educators of color.

“The federation does not challenge the existence of the pandemic, the science of vaccines, the efficacy of vaccines or the seriousness of the surge,” attorney Patrick Bryant, who represents the Boston Police Superior Officers Federation, told GBH News. “We think a testing option, as exists for almost nearly all employers in the public sector and private sector in the state of Massachusetts, is effective. In fact, we asked Mayor Wu to increase the testing opportunities for our members, both vaccinated and unvaccinated, so we can get a handle on the pandemic.”

Wu initially set the deadline for Jan. 15, but pushed it back to Sunday in the face of union opposition.

The mayor said Monday that more than 94% of the city's workforce — or nearly 18,3000 employees — have met the mandate. That includes 94% of public school workers, 95% of police department staff, 95% of library workers, 97% of parks and recreation workers and 91% of fire department staff.

Wu has said her administration is also sifting through more than 600 requests for an exemption based on medical or religious reasons.

GBH News' Mark Herz contributed to this story.