WEST BRIDGEWATER, Mass. (AP) – Shaw’s Supermarkets and the union representing 6,000 workers reached a tentative four-year contract agreement late Thursday night, setting the stage for a member vote Saturday that could prevent or authorize a strike.

Union spokesman Peter Derouen declined to provide details, saying they would not be made available until the members of United Commercial Food Workers Local 791 vote on the pact. Employees at 25 Shaw’s stores in southeastern Massachusetts and 14 in Rhode Island will vote on whether to accept the contract on Saturday in Mansfield.

The agreement was reached late Thursday night with the assistance 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 two sides were in talks on the last day of five-day extension of an expired three-year contract. The talks also cover a 350-employee distribution center in Wells, Maine.

Union members voted overwhelmingly on Sunday to authorize a strike. But they have continued working while negotiators for West Bridgewater-based Shaw’s and the union have met daily with the participation of a federal mediator, often late into the night.

Derouen had said negotiators had resolved some differences in recent days, although sticking points remained.

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 non-unionized 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.