In a written decision in federal court in Brooklyn, U.S. District Judge Nicholas Garaufis said the city had not come up with a good explanation for wanting to hire a new class of firefighters based on an "invalid" test.
"Before the court can permit the city to use (the current exam) in any manner, the city must explain what has changed and why the need to appoint a few hundred rookie firefighters outweighs the need to avoid racial discrimination in municipal hiring," the judge wrote.
The judge's order prohibits any new hiring until Oct. 1. The judge said he would soon schedule a hearing to consider "remedial measures" to meet the city's needs.
A city lawyer, Georgia Pestana, warned in a statement Wednesday that the city will be forced to pay $2 million per month in overtime to make up for understaffing at the 11,000-member fire department.
"We are extremely disappointed in today's decision and are evaluating all legal options," Pestana said.
The ruling follows earlier setbacks for the city in the lengthy legal dispute with the federal government over discrimination claims. The judge previously found the FDNY had deliberately discriminated against minorities and ordered it to revamp its hiring practices.
The U.S. Department of Justice sued the city in 2007, alleging the fire department was using exams that were littered with SAT-like questions that failed to fairly measure an applicant's ability to fight fires. The lawsuit was prompted by what critics describe as the department's woeful record on minority recruitment when compared with other big city departments.