ROCKLAND, Maine — Negotiations between the city and its largest labor union are headed to mediation.

Rockland City Manager James Smith said Tuesday that no date for the first mediation session has been set although a mediator has been selected.

Smith said the ball was in the union’s court and referred questions about what has led to mediation to the Teamsters Union. A telephone message was left Tuesday with the union representative.

In July, the city reached a contract agreement with its firefighters union. In that three-year contract, the 12 firefighters covered by the pact agreed to pay a larger share of health insurance premiums. The former contract and a city ordinance had both specified that the city would pay 85 percent of premiums while the employees would pick up 15 percent.

The council voted in July to revise that ordinance so that the percentage breakdown would be determined during contract talks.

Firefighters agreed to pay 20 percent of the premiums by the third year of the contract.

The Teamsters represent the city’s police officers, public works employees, clerical workers and staff at the wastewater treatment plant.

When he introduced his 2012-2013 budget five months ago, Smith had said there would be a pay freeze for all employees until union contracts were settled. He also said in his May budget message to councilors that he would call for a restructuring of health insurance programs, although he did not provide specifics.

The city has since granted 2.5 percent raises to its department heads and other nonunion workers.

Smith said Wednesday he thought that he could reach an agreement with the unions sooner.

“However, at the point in time when I realized that it was going to take longer to settle the terms of an agreement with the Teamsters, I decided that nonunion employees need not wait any longer for a pay adjustment. In short, it did not make sense to withhold pay adjustments to nonunion employees until we could settle our contract with the Teamsters,” Smith said.

The city council is scheduled to decide next Wednesday night what percentage raises to give to the city manager, city attorney and city clerk. Those three positions are hired by the council.