The notices give the attorney general's office 60 days to take up the case on behalf of all Californians. If the state declines to pursue the matter, the group said in the documents that "it intends to bring suit in the public interest" against the companies.

Under California law, companies are required to warn consumers if their products contain known carcinogens.

The chemical in question, acrylamide, is formed when starchy foods are baked or fried at high temperatures. Acrylamide is listed by the California Office of Environmental Health Hazard Assessment as a chemical known to cause cancer.

The US Food and Drug Administration has been studying the impact of acrylamide levels in food since 2002. On its Web site, the FDA said that, while the chemical is known to cause cancer in laboratory animals in high doses, it is "not clear whether acrylamide causes cancer in humans at the much lower levels found in food."

"At this point we're still trying to evaluate the effects of acrylamide," said FDA spokesman Mike Herndon.

PepsiCo unit Frito-Lay said in a statement that it has not yet received the notice from the ELF, but said its "food safety standards are very stringent and meet all federal and state regulations."

Pringles spokeswoman Kay Puryear said its products "are as safe as ever" and that Procter & Gamble has been "working to reduce the formation of acrylamide."

A Kettle Foods spokeswoman said the company would not comment on pending litigation.

Officials at Lance were not immediately available for comment.

According to the Oakland, California-based Environmental Law Foundation, tests it commissioned found levels of acrylamide in many of the nation's most popular potato chip brands far exceeded the levels requiring warning labels under California law.