Contract talks between Buffalo firefighters and negotiators for Mayor Byron W. Brown took a combative turn when city bargainers “stormed out” of a session, the fire union president said Thursday.

The contentious meeting took place Wednesday, when the union unveiled a proposal that spanned 11 fiscal years, from 2002 to 2012. It called for a retroactive $5,000 increase in firefighters’ base salaries, then annual raises ranging from 3 percent to 3.4 percent over 10 years.

Union President Daniel Cunningham said the plan included a key concession that would require all firefighters hired in the future to live in the city for the duration of their careers.

“It would add to the quality of life in the City of Buffalo and increase its tax base,” Cunningham said.

But the bargaining session didn’t get very far, he added, claiming a seven-member city bargaining team hastily retrieved its belongings and left.

“They just stormed out,” Cunningham said. “It wasn’t very professional. But it didn’t surprise me.”

Brown administration officials said they do not discuss ongoing contract negotiations. But Finance Commissioner Janet Penksa told The Buffalo News the union’s offer was fiscally unrealistic.

“The union leadership gave us a proposal that would bankrupt the city,” was all Penksa would say.

Neither Penksa nor the mayor took part in Wednesday’s bargaining session.

The budget office did not release projections on how much the raises would cost, nor would officials discuss proposals offered by the city. Cunningham said the city’s latest offer would have given raises totaling 13.5 percent over 11 fiscal years, and there would be a separate lower-pay tier for new hires.

The union president said one aspect of the city’s proposal would “eliminate a nationally recommended” minimum staffing requirement that calls for each fire vehicle to be staffed by four individuals.

“They want to destroy a national review standard, risking the safety of the firefighters and also the residents of the City of Buffalo,” Cunningham said.

Peter K. Cutler, the mayor’s chief spokesman, wouldn’t comment, saying the administration doesn’t feel it’s “ethical” for negotiators to divulge details of ongoing contract talks.

The union has maintained that even with the recent hiring of new firefighters, the department has lost more than 160 jobs since 2002 as the city closed multiple firehouses and deactivated 10 fire companies — or trucks.

Cunningham took issue with Penksa’s claim that the union’s latest offer would “bankrupt” Buffalo, saying the city has been racking up record surpluses. Starting July 1, the city will start using some reserves to balance the budget.

Firefighters have been working under the terms of an expired contract for eight years. But in some prior interviews, Brown was quick to note that firefighters voted down two proposed agreements in 2007 and 2008. While the mayor had insisted the offers were fair, union leaders said concessions overshadowed raises that workers would have received.