SAN DIEGO -- For the fourth day, about 70,000 unionized workers continue to picket outside three supermarket chains: Ralphs, Vons and Alberstons.

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Seven local chapters of the union representing striking supermarket workers are suing Albertsons and Ralphs for locking out employees in response to the job action against Vons.

The local chapters of the United Food and Commercial Workers International Union claim the lockout is a violation of California's Mass Layoff Notification Law, and are seeking millions of dollars in back pay for health care and pension payments.

While many grocery story employees are praising the action, Mark Bennett, a management and labor attorney, does not believe that the suit has merit.

"I don't think it's going to hold up in court because I don't think that what's happening fits within the definition of a layoff under state law," said Bennett.

The law, passed in 2002, requires that every employee individually be given 60 days' notice prior to any mass layoff.

Bennet said, "Layoff is defined under state law as a separation of employment because of a lack of funds with a lack of work. These employees are not separated from their employment, whether they are locked out or whether they are on strike. Under federal law they are still considered to be employees of the chains that they work for. They are not fired and they have rights to go back to work with the strike is over."

In the current labor dispute spearheaded by seven Southern California UFCW locals, a strike against Vons is in its fourth day.

Ralphs and Albertsons have locked out their employees.

The unions estimate that the amount owed their union members locked out by the two employers exceeds $600 million.

The employers have 30 days to respond to the lawsuit.