(Lancaster) -- The city of Lancaster and its firefighers union will seek binding arbitration to resolve disputes over a labor contract. Mayor Rick Gray says International Association of Firefighters Local 319 has declared an impasse in the negotiations. He says some of the main disagreements are over staffing levels, the hiring of part-time firefighers and the use of volunteers for back-up. "We just want to utilize the personnel better, so that they're there for their own safety and also the public's safety when there is a critical emergency," he says. "Also from a safety perspective, that they have appropriate backup that we can afford." Gray says requests for wage increases are also an issue because 95 percent of the department's roughly $10 million annual budget is made up of personnel costs. On a statement on the union's website, it says its proposals aimed to balance city budget concerns with public safety. Three arbiters will review the dispute.