Attorney General Bill Lockyer asked for a court order requiring McDonald's, Burger King, Wendy's, Frito Lay and other companies to warn consumers that their fries and chips may contain acrylamide, a chemical the state says causes cancer.
At least one of the companies disputes that, saying there is no evidence the substance is carcinogenic.
"In taking this action, I am not telling people to stop eating potato chips or french fries," Lockyer said. "I know from personal experience that, while these snacks may not be a necessary part of a healthy diet, they sure taste good."
But consumers should have the information needed to make informed decisions about their food, he said.
Acrylamide, a byproduct of chemicals and high heat, has been found at low levels in several foods. The lawsuit focuses on french fries and chips because they have more acrylamide than other foods, according to the Attorney General's Office.
Frito-Lay spokeswoman Lynn Markley said there was no scientific evidence that acrylamide causes cancer. She said it was counterproductive for the state to sue the companies when California regulators are setting standards for the chemical under Proposition 65, a state law that requires companies to notify the public about potentially dangerous toxins in food.
When risk levels for acrylamide were added to Proposition 65 in 1990, the chemical was generally thought of as an industrial agent, used in food packaging and to treat sewage, according to the U.S. Department of Health and Human Services.
But in 2002, a Swedish National Food Authority study reported that acrylamide occurred naturally in some starch-rich foods as a result of cooking or heat processing.
Other studies have found no link between foods containing acrylamide and a higher risk of cancer.
The U.S. Food and Drug Administration is currently assessing the chemical in food.
Representatives of other companies named in the lawsuit did not return calls for comment Friday. The lawsuit was filed after business hours in the Central and Eastern time zones.
Teresa Schilling, a spokeswoman for the attorney general, said that if the lawsuit succeeds the office will want to discuss with the companies the size of the warning labels and where they would appear on packaging.
"We don't want the warning to be alarming or excessively large," she said. "We want it to be simple and effective, and (we'll) be flexible about how it will work with each product."