BATH – Union leaders at Bath Iron Works are angry about the company’s plan to lay off maintenance workers and hire a private company to clean offices, take care of the grounds and perform other maintenance tasks.

BIW plans to make the change in mid-July, according to officials of the local S6 of the International Association of Machinists and Aerospace Workers, the largest union at the shipbuilder.

Although the change would result in the elimination of just 24 jobs, union officials said it would set a precedent for more job outsourcing in the future. They said the move violates the four-year labor contract the union and company agreed to a year ago and could extend to other positions beyond maintenance workers.

Mike Keenan, president of the 3,850-member union, said members blame the dispute on BIW President Dugan Shipway. Keenan said the union’s biweekly meetings with Shipway have ended.

“Let there be no doubt, the union agrees we have to be competitive,” Keenan said. “This is not how you become competitive.”

BIW spokesman Dirk Lesko said the company had no comment on what he called ongoing negotiations.

The disagreement comes at a time when the shipyard’s future is unclear, with the Navy proposing major changes in its plans for the next-generation destroyer. It also comes as companies nationwide are increasingly hiring outside contractors to reduce operating costs.

BIW, which has a work force of about 5,800, has laid off workers over the past year to cut costs. But those cuts were due to lack of work, Keenan said.

BIW’s plan to use outside employees from a Massachusetts company for maintenance work is different, union officials said.

“They’re going after jobs they still have the work for – that’s our work,” said Charlie Finn, chairman of the union’s legislative committee.

The company has brought in subcontracted labor before, said Keenan, but has always discussed the plans with the union.

In most cases, the union agreed the temporary jobs could be filled with outside labor, he said. In other cases, the union pointed out problems with the company’s projected cost savings, and jobs instead went to union members.