Mayor Michael Nutter says the cash-strapped city can't afford the award issued by an arbitration panel earlier this month.
The panel gave firefighters three years of 3 percent raises, retroactive to 2009. The ruling also denied the city the right to furlough 2,100 firefighters and medics.
In a statement released Friday, Nutter says the award will cost $200 million. He also says it doesn't meet requirements set by the state agency overseeing Philadelphia's finances.
Firefighters union president Bill Gault says the panel's decision is fair and affordable.
The ruling came after 20 months of legal battles and one appeal by the city. Thousands of firefighters marched on City Hall on Thursday.