Hawaiian Electric Co. and its largest group of unionized workers were continuing to negotiate terms of a new labor agreement yesterday to replace the one that expires at midnight tomorrow.

The contract covers about 1,280 HECO workers on Oahu and at its affiliated utilities on Maui and the Big Island doing a range of jobs, including line work, meter reading and customer service. The workers are members of the International Brotherhood of Electrical Workers Local 1260.

"We are continuing to meet with the union to come up with an agreement that is fair to both our employees and our customers," said HECO spokesman Darren Pai. "We are optimistic that we will be able to achieve that."

Neither the company nor union would comment on the substance of the negotiations.

About 700 of the workers cast ballots in a recent strike authorization vote, which was approved by 97 percent, according to the union.

The vote authorizes union leaders to call for a strike on members’ behalf should it become necessary. Unions often take strike authorization votes as a way to give them more leverage in their negotiations.