LOS ANGELES, Calif.–The union representing thousands of Southern California grocery workers voted to authorize a strike, leaders announced today, but the union would be required to give stores a 72-hour warning if they decide ask workers to walk off the job.

Negotiators plan to be back at the bargaining table next week.

According to the United Food and Commercial Workers Local 770, the vote to authorize a strike was “overwhelming.” Results, in terms of the percentage for and against, however, were not immediately available this morning. Two-thirds approval was required.

The union’s contract with parent companies of Ralphs, Vons and Albertsons expired on March 6. The contract has been extended on a day-to-day basis as negotiations continue.

The existing contract was ratified in 2007 after about seven months of negotiations. In 2003-04, a grocery workers strike and lockout dragged on for 141 days, wiping out the savings of most workers and costing supermarkets an estimated $1.5 billion.