Attorneys for Starbucks Corp. and other coffee sellers have less than two weeks to persuade a Los Angeles County judge to reconsider a proposed ruling that could force them to post cancer warnings in stores and on packages.

Superior Court Judge Elihu Berle, in a tentative decision issued Wednesday after a trial, said Starbucks and dozens of other defendants had failed to prove that the level of acrylamide in their coffee poses no significant health risk.

“Defendants did not offer substantial evidence to quantify any minimum amount of acrylamide in coffee that might be necessary to reduce microbiological contamination or render coffee palatable,” Berle wrote in his proposed statement of decision. He said the proffered evidence that coffee has some health benefit “was not persuasive and was refuted by plaintiffs' evidence.”

Acrylamide, which occurs naturally in the bean-roasting process, is listed as a potential reproductive and cancer risk under California's Proposition 65. The 31-year-old voter-approved law requires businesses to warn consumers when they are exposed to one of approximately 900 state-listed chemicals. Those that don't comply can be sued and face civil penalties of up to $2,500 per day, per violation.

The National Coffee Association said industry members are considering their options, including “potential appeals.” Warning labels on coffee would be misleading, the statement said.

“Coffee has been shown, over and over again, to be a healthy beverage,” association president and CEO William Murray said in a statement. “This lawsuit has made a mockery of Prop 65, has confused consumers, and does nothing to improve public health.”

Raphael Metzger, the attorney for plaintiff Center for Education and Research on Toxics, or CERT, noted in an email message that Berle's decision is not yet final.

“Generally, manufacturers need to … put the warnings on packages (bags/cans) of coffee,” Metzger said. “Retailers need to post point-of-display warnings.”

CERT will ask a judge to determine civil penalties, if the decision becomes final, he said.

Joshua Bloom, a partner at Meyers Nave Riback Silver & Wilson in Oakland, said the case and its ultimate disposition are significant both in the scope of the number of businesses and coffee drinkers that could be affected and the potential for shaping Prop 65 enforcement in the area of prepared foods.

“We're not just talking about booster cables or clotheslines or any of a thousand other consumer products,” Bloom said. “First, you're talking about a food product—things that people ingest, where there's understandably a heightened level of scrutiny. And second, it's coffee.”

Many California coffee shops already post Prop 65 warning signs, a move potentially aimed at capping any penalties should the CERT litigation, which started in 2010, succeed, Bloom said.

Prop 65 is a regular target of business groups who say its private-right-of-action provisions and far-ranging scope leads retailers and manufacturers to post so many warning signs that consumers have come to ignore them.

James Colopy, an environmental litigation partner at Farella Braun + Martel, said the decision points to flaws in Prop 65 because “science does not support” a hazardous “level of connection between acrylamide and cancer or reproductive toxicity.”

“The law is very broad and that's the takeaway in this decision,” Colopy said. “This is not judicial overreach. This is a judge enforcing the law on the books.”