The case being heard in an Oakland court has been brought on behalf of 115,919 current and former Wal-Mart employees. Fred Furth, the lawyer for the plaintiffs, said that for years most employees dared not ask management about missed meal breaks. "Some of the braver ones did ask, and I'm going to prove Wal-Mart ignored their pleas to hire more help," he said.

The trial comes at a time when the Arkansas-based company is already grappling with some 40 different legal actions to do with its employment policies. Most daunting is a pending class-action suit claiming the company routinely paid female workers less than male workers.

Only last week, a workers' rights advocacy group, the International Labour Rights Fund, said it filed a lawsuit in Los Angeles against Wal-Mart on behalf of hundreds of workers abroad who wereexploited by companies supplying goods to the retailer.

In that suit, Wal-Mart is accused of ignoring the abuse of workers in foreign factories because of its desire to find cheap supplies. The company, like many other retailers, has established its own code of conduct to guard against abuse.

Terry Collingsworth of the Labour Rights Fund said the case would be a test of whether codes of conduct drafted by corporations such as Wal-Mart were "simply public relations devices or whether they mean what they say". The suit describes a woman in Bangladesh who worked from 7.45am to 10pm and was not given a day off in six months.

In Quebec a government labour relations board found against Wal-Mart this week for closing down a store outside the town of Jonquiere. The company said the outlet was not profitable, but board members suggested the real reason was because workers had successfully unionised there and Wal-Mart was not prepared to deal with unionised employees. The company faces a large fine.

These legal entanglements amount to a public relations nightmare for Wal-Mart, which in recent months has met resistance in trying to open in new locations, notably in New York City and Los Angeles.