WEST BRIDGEWATER, Mass. – The union representing more than 6,000 grocery workers will vote Saturday on a tentative contract agreement after negotiators reached a last-minute deal with Shaw’s Supermarkets, likely averting a threatened strike.

Members of United Commercial Food Workers Local 791 struck the deal with Shaw’s late Thursday night, with the help of a federal mediator.

“We were able to reach agreement on a fair contract which allows Shaw’s to be even more competitive … while providing our associates excellent wage increases and affordable, high-quality health care,” the company said in a statement.

The union, which covers 25 Shaw’s stores in southeastern Massachusetts and 14 in Rhode Island, as well as 350 employees at a distribution center in Wells voted overwhelmingly last Sunday to authorize a strike. But they continued working under their old contract while negotiators for West Bridgewater-based Shaw’s and the union met daily with the mediator, often late into the night.

Earlier in the week, the two sides agreed to extend by five days the previous three-year contract, which expired last Saturday. That extension was scheduled to end at midnight Thursday.

Union spokesman Peter Derouen declined to provide details of the new contract, saying they would not be made available until the membership takes its ratification vote on Saturday in Mansfield.

Negotiators have been meeting since June to try to resolve differences over issues including health care costs, wages, work rules and pension benefits.

Workers at other Shaw’s stores in Massachusetts, Maine, New Hampshire and Vermont are nonunionized and unaffected by the labor talks. Unionized Shaw’s employees in Connecticut are covered by a different local.

Shaw’s is owned by Boise, Idaho-based Albertsons Inc., one of the nation’s largest food and drug retailers.