The union representing some 60,000 grocery workers in Southern California is escalating the pressure on the region’s big supermarket chains, as shoppers wait to see if picketers will gather at their favorite stores.

Members of the United Food and Commercial Workers voted overwhelmingly to authorize a strike last week, giving union leaders the power to pull its workers out of Ralphs, Vons Albertsons and Pavilions stores.

Union members will ask shoppers on Wednesday to boycott three stores for a two-hour period to gauge public support.

On Monday, the executive board of the Los Angeles Federation of Labor voted unanimously for sanctions that endorsed a UFCW strike, meaning members of 300 private- and public-sector unions in Los Angeles County will not cross picket lines. That commitment amounts to some 800,000 unionized workers and their families.

“That’s a large chunk of consumers who are going to show their displeasure,” said Mike Shimpock, spokesman for Los Angeles-based Local 770.

Deliveries also could stall if Teamster truck drivers also decline to cross UFCW picket lines, Shimpock said.

When 31,000 workers at the New England chain Stop & Shop went on strike for 11 days in April, the Teamsters’ endorsement led to virtually empty store shelves, Shimpock said.

Randy Cammack, president of Joint Council 42 of the Teamsters, said the sanctions would give union drivers the option but no mandate not to cross picket lines. He added that sanctions could also be added to cover pickets at food distribution centers.

Representatives of the four stores did not reply to requests for comment.

The LAFL’s endorsement now goes to the organization’s board of delegates, which consists of a representative from all 300 union locals. Shimpock said that group will probably vote on the issue within two weeks.

Local 324, which represents Orange County workers, will position people at tables outside two selected stores and urge shoppers to boycott these stores — a Ralphs in Garden Grove and a Pavilions in Long Beach — for two hours, from 3 to 5 p.m. on Wednesday. A similar effort will take place Wednesday at an Albertsons in Redlands.

“We just want to see what kind of support we’ll get from shoppers,” said Greg Conger, president of Local 324.

Union members authorized the strike after almost four months of stalled negotiations because the chains’ best offer would cut cashiers’ pay by 25% by downgrading their job classifications. Other store employees would get raises of only about 1%, and union leaders have pointed to pay increases for senior executives at Kroger Co., Ralphs’ corporate parent, are as high as 34%.

Also, UFCW claims proposed cuts in what the chains pay into the workers’ health insurance pool could cause those funds to dry up.

The success of labor action by the Southern California locals would largely depend on support from shoppers, some of whom seem sympathetic to UFCW’s efforts.

Holly Ober, a Riverside resident who was shopping in the Ralphs store in the Canyon Crest area late last week, has a labor background from her years on the UC Davis faculty.

“I would not cross a picket line,” Ober said. “If they believe they need to strike I would support them.”

The current dispute reminds many of the strike and lockout of 2003 and 2004, when workers walked picket lines for more than four months. Alexandra Moreno was a teen growing up in Pasadena then, but she remembers shopping with her mother, who tried to avoid stores with striking workers.

Moreno, a Moreno Valley resident, said that while understands the workers’ situation, her decisions on where to shop often are more focused on products that are only available at certain stores, along with pricing.

Ron Steen, a Menifee resident loading his trunk at the Riverside Sprouts, a non-union store, said the UFCW may be disappointed by the public’s reaction this time.

“I think that maybe people won’t be as excited if they go on strike than they were previously,” Steen said. “There are so many additional stores now, like this one.”

Craig Rosenblum, a retail analyst with consulting firm Willard Bishop, said it was common for non-union stores to enjoy sales spikes during a labor reaction, although the long-term market shifts tend to vary.

“For the most part, in today’s market, it’s pretty much about value, convenience and experience,” said Rosenblum about shoppers’ choices. “If any of these are impacted, shoppers go somewhere else.”