Talks with a federal labor mediator Friday were not successful in resolving differences that the city’s police and fire department forces have with City Hall.

According to a statement released Friday evening by the Lawrence Professional Firefighters organization, the police and fire groups remain at an impasse in their negotiations for a new work agreement with the city.

At issue is the amount of longevity pay that city employees should receive. In response to an economic slowdown, the city has proposed reducing by half the annual longevity payment made to employees with five or more years of service. The payment would be cut from $48 per year to $24 per year.

Leaders with both organizations said a lingering labor dispute could create problems, such as a decline in employee morale.