The law, Proposition 65, requires warning labels on products that cause cancer or harm the reproductive system.

There is currently no federal policy requiring labels for genetically altered goods.

The one bill that did pass last year was in Mississippi, which required more extensive labels on bags of genetically modified seeds.

A second measure would require labels identifying genetically engineered foods sold in the state.

Their legislation would also require labels that are more readable for all Americans.

But critics have said the California warnings are not strong enough, and the two states require different labels.

Thailand is alone among countries in requiring labels to list ingredients by percentage.

Last year, the state began carrying out a law passed by voters that requires labels warning of possible exposure to toxic substances.

Complex subjects, like multi-word terms, may require labels which contain many words.

A law passed by popular ballot in 1986 requires warning labels on any food whose ingredients have a 1-in-100,000 chance of causing cancer.