A cup of coffee could soon come with a cancer warning in California where mediation is starting Thursday as part of a highly-charged lawsuit. The Council for Education and Research on Toxics wants businesses to warn consumers about a possible cancer risk from coffee. The lawsuit, which has been grinding on for years, alleges no matter how you make it, your daily jolt of java comes with a potential carcinogen: acrylamide.

Bill Ristenpart, a chemical engineer, teaches the science of coffee at UC Davis. As an expert witness, he testified that acrylamide forms naturally as foods cooked at high temperatures turn brown, reports CBS News' John Blackstone.

"It's the major reason you get this yummy brown stuff on the outside of your steak when you char it," Ristenpart said.

But in high doses, acrylamide has been found to cause cancer in mice. That puts it on a list of cancer-causing chemicals that businesses in California are required to alert consumers about thanks to a law passed in 1986.

Coffee shops are being sued under California's Proposition 65 which forces them to post warning signs all over the place. The trouble is, in California, cancer seems to be brewing everywhere. At least it seems that way if you pay any attention to those warning signs.

Park your car in an indoor garage and you are likely to find one. At any place that sells alcohol, the writing's on the wall. It's posted at the happiest place on earth and even outside CBS News Los Angeles.

"They create in some people concern that there's something lurking in places and they don't know what it is," said UC Hastings law professor, Marsha Cohen.

But the potential coffee warning may be stretching the intention of the law.

"I believe in transparency but at the same time when you put a bold declaration, x may cause cancer when there isn't data to that effect in humans, to me, it causes panic rather than informed knowledge," said CBS News medical contributor and cancer expert Dr. David Agus.

In a statement, the National Coffee Association told CBS News: "This lawsuit simply confuses consumers, and has the potential to make a mockery of Prop 65 cancer warnings at a time when the public needs clear and accurate information about health."

Thirteen defendants, including Gloria Jean's and 7-11, have settled and agreed to put up the signs. Starbucks is still waging a legal battle, arguing that coffee has health benefits.

"Coffee in moderation has been shown to potentially decrease the risk of certain cancers and potentially to have some heart benefit," Agus said.

These warning signs might be one coffee order that Californians will have some trouble swallowing.