Initiative Will Test Appetite for GMO Food Calories. Nutrients. Serving size. How about "produced with genetic engineering?" California voters will soon decide whether to require certain raw and processed foods to carry such a label. In a closely watched test of consumers' appetite for genetically modified foods, the special label is being pushed by organic farmers and advocates who are concerned about what people eat even though the federal government and many scientists contend such foods are safe. More than just food packaging is at stake. The outcome could reverberate through American agriculture, which has long tinkered with the genes of plants to reduce disease, ward off insects and boost the food supply. International food and chemical conglomerates, including Monsanto Co. and DuPont Co., have contributed about $35 million to defeat Proposition 37 on the November ballot. It also would ban labeling or advertising genetically altered food as "natural." Its supporters have raised just about one-tenth of that amount. If voters approve the initiative, California would become the first state to require disclosure of a broad range of foods containing genetically modified organisms, or GMOs. Food makers would have to add a label or reformulate their products to avoid it. Supermarkets would be charged with making sure their shelves are stocked with correctly labeled items. A product labeled with Non Genetically Modified Organism (GMO) is sold at the Lassens Natural Foods & Vitamins store in Los Feliz district of Los Angeles Friday, Oct. 5, 2012. International food and chemical conglomerates are spending millions to defeat California's Proposition 37, which would require labeling on all food made with altered genetic material. It also would prohibit labeling or advertising such food as "natural." (AP Photo/Damian Dovarganes) Close Genetically altered plants grown from seeds engineered in the laboratory have been a mainstay for more than a decade. Much of the corn, soybean, sugar beets and cotton cultivated in the United States today have been tweaked to resist pesticides or insects. Most of the biotech crops are used for animal feed or as ingredients in processed foods including cookies, cereal, potato chips and salad dressing. Proponents say explicit labeling gives consumers information about how a product is made and allows them to decide whether to choose foods with genetically modified ingredients. They're fed up. They want to know what's in their food," said Stacy Malkan, spokeswoman for the California Right to Know campaign. Agribusiness, farmers and retailers oppose the initiative, claiming it would lead to higher grocery bills and leave the state open to frivolous lawsuits. Kathy Fairbanks, spokeswoman for the No on 37 campaign, said labels would be interpreted as a warning and confuse shoppers. It's not necessary. Worse, it leaves people with the impression that there's something wrong with the food. That's not the case," she said. The government approves genetically engineered plants and animals on a case-by-case basis, and the U.S. Department of Agriculture restricts the use of GMO crops that might harm other plants. The Food and Drug Administration can only require labeling if a genetically altered food is different - in taste, for example - from its non-engineered version or known to cause allergies. The World Health Organization has said no ill health effects have resulted from GMO foods currently on the international market. The American Medical Association sees "no scientific justification for special labeling of bioengineered foods" but favors stricter testing before they hit stores. Still, some consumers are wary and are increasingly demanding to know what's on their dinner plates. With California a trendsetter on other issues, whatever happens in the nation's most populous state could spill onto the national stage.