The union representing 62,000 grocery workers in southern California has received the go-ahead from members to call a strike if an acceptable contract deal cannot be reached with Ralphs, Vons and Albertsons supermarkets, officials said on Sunday.

Over 90 percent of workers voted on Friday and Saturday to authorize a strike, far in excess of the two-thirds vote required, the United Food and Commercial Workers union said.

Mickey Kasparian, the president of UFCW Local 135, said a federal mediator would continue to work toward a resolution, but a strike could be called in five or six days if there were no positive developments.

If we don't get a deal, we'll take this fight to the streets, Kasparian said.

Mike Shimpock, a spokesman for UFCW Local 770, the biggest of the seven union branches that are poised to strike, said there are no talks scheduled with the supermarkets.

The union is obligated to give the companies at least 72 hours notice before workers can strike, he said.

In 2003, southern California played host to the longest work stoppage in the history of the U.S. grocery industry. That bitter, four-and-a-half-month standoff shifted more than $1 billion in sales, and the loyalty of some shoppers, to competitors.

A contract between the supermarkets and unionized workers expired in March. While the union workers previously voted to authorize a strike, changes to offers being negotiated made another vote necessary.

Ralphs owner Kroger Co (KR.N), Vons owner Safeway Inc (SWY.N) and Albertsons owner Supervalu (SVU.N) are negotiating as a group.

Kendra Doyel, a spokeswoman for the grocery chains, said the strike authorization vote is a common negotiating tactic and does not necessarily mean the union will call a strike.

Ralphs, Vons and Albertsons remain committed to reaching a contract that is good for our employees and keeps these union jobs sustainable for the future, Doyel said in a statement.

The two sides have a tentative agreement on pensions, but the main point of dispute is healthcare coverage.

Under the latest offer from the stores, workers would pay a premium of $9 a week for individual coverage, and $23 a week for a family, company and union officials said.

But the union wants the supermarkets to contribute more to a health fund it says will run out of money in about a year. Meanwhile, no deal has been reached on wages.

Southern California, a supermarket union stronghold, is one of the most competitive grocery markets in the United States.