The union and the mayor have been at odds for years over the contract and a series of cost-cutting moves the administration has imposed - particularly the rolling closures of fire stations known as "brownouts."
The union's contract expired in July 2009. Because firefighters and police are prohibited from going on strike, disputes go to a three-member arbitration panel for a ruling.
Arbitrators awarded a contract in 2010 that the administration appealed as financially ruinous, costing $31 million a year when the city was counting on savings.
After a year, a Common Pleas Court judge sent the case back to the arbitration panel for reconsideration. The panel this month awarded 3 percent raises and denied the city the right to furlough firefighters and medics.
The union argues that the administration is out of options. "They now have no statutory grounds for seeking another level of review," says the lawsuit, filed in Common Pleas Court.
The actual costs of the latest award remain in dispute - the administration agrees with its representative on the arbitration panel, who said the contract contains "more than $200 million in unbudgeted costs." Gault said the contract would cost $16 million in raises a year, but the city has squeezed $15 million in annual savings from the Fire Department.
Nutter has not tipped his hand, but if he decides to appeal he could cite his belief that the contract is not affordable.
Mark McDonald, the mayor's spokesman, said the administration still was evaluating the contract. Of the lawsuit, he said:
"The beauty of the American legal system is, it offers any party the opportunity to file a lawsuit. Local 22 has availed itself of that."
This month Gault wrote to Nutter urging him to sign the contract and asking him to appear with him next week at the International Association of Fire Fighters' annual convention, being held in Philadelphia this year.
Gault said another appeal "will most definitely be viewed as an insult to the firefighters, paramedics, and their families in attendance." He said Nutter had not responded.
Union general president Harold A. Schaitberger, who joined Gault to discuss the lawsuit, said the 3,000 firefighters expected to attend the convention "are going to be standing in solidarity" to ensure Nutter signs the contract.
"If not, as we say in the business, we got your back," Schaitberger said.
Contact Troy Graham at 215-854-2730 or firstname.lastname@example.org, or follow on Twitter @troyjgraham.