Representatives from Hawaiian Electric Co. and its largest group of unionized workers reached a tentative agreement yesterday on a new labor agreement to replace one that expired three months ago.

Members of the International Brotherhood of Electrical Workers Local 1260 had been working under an extension since Oct. 31, 2010, when the original contract expired. The extension was due to expire last night at midnight. The tentative agreement will be put to the union membership for a ratification vote that has yet to be scheduled.

Details of the agreement were not immediately available.

The contract covers about 1,280 workers at HECO on Oahu, Maui Electric Co. and Hawaii Electric Light Co. on the Big Island, doing a range of jobs, including power plant operations, line work, meter reading and customer service. The IBEW represents 54 percent of the company’s 2,380 workers on three islands.

The union members authorized a strike in a vote last fall before the original contract expired.

Union officials did not return calls seeking comment yesterday.

This isn’t the first time negotiations between HECO and Local 1260 have extended past the original contract expiration date. The previous contract ended on Oct. 31, 2007, but the two sides did not reach agreement on a new pact until March 2008. Union members did not strike during those negotiations.