Steve Berman, whose firm Hagens Berman Sobol Shapiro LLP is behind most of the cases, said suing on behalf of consumers instead of victims of forced labor avoided questions over jurisdiction. He said the judge was wrong and that he’d appeal.

For their part, the companies Berman sued reject that they can be held responsible for the actions of “sub-suppliers.” In court filings, they say corporate declarations to fight slave labor aren’t guarantees it won’t exist somewhere in the supply chain.

They also caution that the litigation could have unintended consequences, driving companies from countries where their presence allows them to push labor reforms.

‘Trash Fish’

Seafood export is a multibillion-dollar industry in Thailand, providing not only food for human consumption around the globe but ingredients for a wide spectrum of products. Costco, based in Issaquah, Washington, was sued because it sells Thai farmed shrimp bred on fishmeal -- ground-up pieces of “trash fish.” It’s that shrimp food which consumer lawyers say is caught by forced labor, on fishing boats operating far offshore.

“Allegations concerning issues in the Thai seafood industry have been well publicized,” said Richard Galanti, a spokesman for Costco. The company says it performs surprise third-party audits and requires suppliers agree to a ban on forced labor. But even with those policies, transparency is a daunting, if not impossible task, say two lawyers who advise companies on such issues but aren’t involved in the lawsuits.

“Everything you see that’s made with mass or substance at some point in its supply chain comes from farming, hunting or a harvesting operation that’s family owned,” said Sarah Rathke, a lawyer with Squire Patton Boggs LLP. “It’s nearly impossible for companies to trace material to that level, because it’s usually collected from the farm and combined with the output of others from nearby.”

Amy Pierce, of the Pillsbury law firm, said local officials are better positioned to regulate labor practices. A European Parliament report said that reality also provides corporations with a level of plausible deniability.

“Slave-made commodities are knowingly blended with those from legitimate sources,” the 2013 report states. “Willful ignorance means that records are kept only in general and innocuous ways in order to conceal the origin of goods.”

Chocolate Industry

In lawsuits against chocolate makers, the problem isn’t trash fish, but cocoa from Ivory Coast, the industry’s biggest supplier. The U.S. has said thousands of children as young as 10 are forced to work there in dangerous conditions.

Boys from “Ghana, Mali, Burkina Faso, Benin and Togo, are found in Cote d’Ivoire in forced agricultural labor,” according to a government report. A self-imposed deadline by chocolate makers to end child slavery among suppliers has been repeatedly extended, most recently until 2020, according to the lawsuits.

Nestle says it has set up pilot monitoring programs on some Ivory Coast farms, with plans to extend to all suppliers by the end of 2016. Hershey and Mars made similar statements, saying that while the lawsuits are without merit, they’re spending hundreds of millions of dollars to eradicate the practice from their supply chains. Mars spokesman Jonathan Mudd didn’t return calls or e-mails seeking comment.

Poverty is a “fundamental issue” in the cocoa growing region of West Africa, said Jeff Beckman, a spokesman for Hershey. Companies across the cocoa supply chain have been involved in initiatives to improve economic, social and labor conditions, he said.

“The pace of change, however, is slower than we would like to see because the underlying issues are complex and have deep economic, social and political roots,” Beckman said.

Second Front

Such reform efforts may have come too late to silence the growing clamor for regulation.

U.S. Representative Carolyn B. Maloney, a New York Democrat who made supply chain slavery one of her key issues, wants to apply the California example nationwide. And she wants to get the Securities and Exchange Commission involved.