Southern California unions and supermarket operators will negotiate through the weekend in a last-ditch bid to end an escalating Southern California supermarket labor dispute that could usher in the region's first grocery strike since 2003.

The union representing 62,000 workers at Ralphs, Vons and Albertsons supermarkets in Southern California issued late on Thursday a 72-hour notice of its plan to cancel its extended contract. The move, aimed at exerting pressure on grocers, clears the way for a strike.

The grocery workers have been without a contract since it expired in March. The two sides still are far apart on wages, but the biggest point of contention is company contributions to employee healthcare.

We just had to draw the line, said John Grant, secretary-treasurer of the United Food and Commercial Workers Local 770, the largest of the union locals representing employees.

Tensions are running high in the region, which was host in 2003 to the longest work stoppage in the history of the U.S. grocery industry. That contentious 4 1/2-month standoff accounted for an estimated $1.5 billion in lost sales to competing stores and permanently shifted the loyalties of some shoppers.

Canceling the contract does not mean workers will walk off the job on Monday, but does clear the way for the union to declare a strike and for retailers to lock-out union workers.

Ralphs owner Kroger Co, Vons owner Safeway Inc and Albertsons parent Supervalu Inc for years have jointly negotiated labor contracts in Southern California.

We continue to negotiate and are extremely focused on bargaining and working toward an agreement -- and that is what is most important right now, said Supervalu spokesman Jeff Swanson.

Workers, who were preparing picket signs and making other strike preparations on Friday, said they were grateful for their jobs, hopeful for a resolution and determined to strike if talks break down.

If I don't stand up for myself now, who will stand up for me in the future? said Tom Hancock, 55, a checker who works at a Safeway-owned store in Hollywood.