NORTHAMPTON - The union representing Northampton firefighters and captains is suing the city over nonpayment of raises they claim are owed to 33 of its newest members.

The lawsuit, filed Tuesday in Hampshire Superior Court by Northampton Firefighters Local 108, contends the city is shirking its legal obligations to pay the raises, known as step increases, to firefighters as they gain seniority and experience.

The step system calls for firefighters and captains to earn annual raises through the first eight years of service. The raises were scheduled to kick in for about half of the union's 67 members at the start of the current fiscal year, or July 1, 2011.

The city and then-Mayor Clare Higgins, however, froze the raises.

"She said the city didn't have the money," said Local 108 President Michael Hatch, a firefighter and paramedic.

The union claims in its lawsuit that the city's actions violate the collective bargaining agreement between the two sides.

The city also violated state wage laws by withholding wages and state collective bargaining laws by not giving the union a chance to negotiate the changes to its contract, Hatch said.

He said it is unclear how much money firefighters are owed.

The suit asks the city to pay triple the back wages owed to each union member, as well as interest and attorney's fees.

In addition to the city, defendants in the lawsuit are Mayor David J. Narkewicz and Fire Chief Brian Duggan.

Narkewicz Tuesday afternoon said he had not seen the lawsuit but he noted that the decision to freeze step increases was made by Higgins for most unions with contracts under negotiation, including the Department of Public Works and the School Department, both unions which went along with the freeze.

He said if the city is forced to retroactively make those payments going back eight months, he may be forced to lay off employees.

In recent weeks, Narkewicz has said the city has little reserves, and has instituted a spending advisory limiting purchases.

Contract impasse

In a separate development, the union and the city remain deadlocked on a new contract after nearly two years of negotiation. The issue is headed for an arbitration hearing at the end of March, Hatch said. He said details of the sticking points between the two sides are confidential.

Firefighters have been working under the old contract, which expired June 30, 2010.

The lawsuit filed Tuesday and contract negotiations are distinct issues, Hatch said. "The lawsuit is completely separate and unrelated to the ongoing contract negotiations," he said.

Meanwhile, Narkewicz said he has invited the firefighters' union to the bargaining table, but the union has not responded to the invitation.