Thousands of southern and central California grocery workers have started voting on whether to authorize their union to call a strike against several major supermarket chains.

Some 47,000 supermarket workers at Ralphs, Albertsons and other grocery chains in southern California are closer to starting the largest private-sector strike since 74,000 General Motors employees walked off the job in 2007. (CNN) - Around 47,000 union workers at Albertsons, Ralphs and other grocery chains in southern California reached an agreement with the companies Thursday on new contracts that they say improve wages and benefits. In April, 31,000 Stop & Shop workers at 240 stores in New England walked out of their jobs for 10 days. Despite the Stop & Shop strike earlier this year, work stoppages are rare in the grocery industry. Grocery workers often have more leverage in negotiations with employers than other retail workers because groceries are perishable and companies can ill-afford slowdowns, experts say.

Workers at more than 500 California stores are demanding higher pay and a contract that protects their retirement and health benefits. This would not be the first strike by California grocery workers. America's empowered labor movementA grocery workers' strike in California would come at a moment when a growing number of Americans are walking off the job. A California strike would be the second major work stoppage in the grocery industry this year. Union workers in grocery storesA grocery strike in California would be a rare work stoppage in retail.