Workers at an El Super grocery store in East Los Angeles picketed Thursday in what could be a prelude to a strike at a handful of the chain’s locations.

About 575 workers at seven of El Super’s more than 30 Southern California locations are represented by the United Food and Commercial Workers union. They’ve been negotiating a new contract since last year with El Super, a Paramount-based subsidiary of Mexican grocer Grupo Comercial Chedraui.

The previous contract expired in September. The union is demanding more hours for full-time employees, sick leave, higher pay and lower costs for health insurance. Workers voted earlier this month to authorize a strike if negotiations broke down. El Super officials did not return calls for comment.

Southern California’s three major grocery store chains, Ralphs, Vons and Albertsons, earlier this month reached a deal with the same union on a new three-year contract in one of the quietest rounds of grocery-labor negotiations in recent years. Grocery workers at those chains went on strike in 2003 and nearly walked out again in 2011.