The MTA replaces over 2,500 fire extinguishers on city buses.
They were recalled after a number of them were found to be faulty.
The issue was discovered by union workers who were conducting emergency bus inspections at the Flatbush Depot in Brooklyn.
Defective equipment was found on more than a dozen buses, prompting management to check the entire fleet.
An MTA official says the agency coordinated with union leaders to replace the extinguishers quickly.
"We ordered and received thousands of fire extinguishers from around the region in three days and replaced the recalled Kidde extinguishers on all 2,500 buses that had them," the official said.