The man behind the biting documentary “Wal-Mart: The High Cost of Low Price,” has found a new target — three major supermarket chains currently involved in a wage and benefits dispute with their Southern California employees.

On Monday, Robert Greenwald, director of a 2005 film that sought to expose how Wal-Mart forces out local competition, underpays employees and stifles labor organization, called the chief executives of Ralphs, Albertsons and Vons the “gang of three” who have withheld pay raises from their employees for 5 years.

Greenwald told reporters he became involved after learning that 20,000 fewer children of grocery workers had health insurance today than before the current contract (which is now expired) went into effect. Ralphs, Albertsons and Vons are owned by Kroger Co., Supervalu Inc. and Safeway Inc., respectively.

The filmmaker, in conjunction with Brave New Films, has launched a multimedia campaign to bring attention to the labor dispute at supermarketswindle.com.

The parties have been negotiating through a federal mediator since March, when the contract that covers some 65,000 workers in Southern California expired.

Workers have given their local unions authorization to strike if needed and have walked out of negotiations on multiple occasions. One key issue is the two-tier system now in place that created a layer of newer employees who get lower pay and must wait between 12 to 18 months after they are hired to qualify for health insurance.

Asked about Greenwald’s efforts, a spokeswoman for the three grocers said: “We don’t feel this will have any impact on our negotiations or commitment to negotiations.”