The march began at Engine 205 in Brooklyn Heights and culminated with a rally outside City Hall.
With just four weeks to go until the fire companies could be shuttered, firefighters organized their biggest protest yet.
More than 1,000 firefighters marched across the Brooklyn Bridge to City Hall, where they joined up with 5,000 others to rally against the proposed closings, which critics say could affect response times in every borough.
"It will put lives in jeopardy because it will extend the response time of the FDNY," Brooklyn Borough President Marty Markowitz said.
Markowitz has called the proposed cuts an outrage, as eight of the 20 fire companies on the chopping block are in his borough. Public Advocate Bill de Blasio has said that according to his analysis, response times in 18 neighborhoods would rise above the national standard of four minutes.
"Under a plan like this, more lives would be lost," de Blasio said. "It's also fundamentally unfair to say to people in some neighborhoods, you get less. You know, just grin and bear it."
The Uniformed Firefighters Association took out this newspaper ad to announce the rally. It depicts the mayor dressed as the grim reaper. But Bloomberg has insisted the closings, which would save the city about $55 million, won't put anyone in danger.
He's suggested that fewer firefighters are needed because buildings are now safer, and he's pointed out that even though six firehouses closed in 2003, response times and fire deaths are at a new low.
City officials stress the list is preliminary and that no final decision has been made. The budget for fiscal 2012, which begins July 1, is still being negotiated between the City Council and the mayor.