GREAT BARRINGTON, Mass. -- On a recent morning, Cynthia LaPier parked her cart in the cereal aisle of a supermarket. With a glance over her shoulder and a quick check of the ingredients, she plastered several boxes with hand-designed stickers from a roll in her purse.
"Warning," they read. "May Contain GMOs (Genetically Modified Organisms)."
For more than a decade, almost all processed foods in the United States -- cereals, snack foods, salad dressings -- have contained ingredients from plants whose DNA was manipulated in a laboratory.
Regulators and many scientists say these pose no danger. But as Americans ask more pointed questions about what they are eating, popular suspicions about the health and environmental effects of biotechnology are fueling a movement to require that food from genetically modified crops be labeled, if not eliminated.
When asked if they want genetically engineered foods to be labeled, about 9 in 10 Americans said they did, according to a 2010 Thomson Reuters-NPR poll.
Labeling bills have been proposed in more than a dozen states over the past year, and an appeal to the Food and Drug Administration last fall to mandate labels nationally drew more than a million signatures. There is an iPhone app: ShopNoGMO.
The most closely watched labeling effort is a proposed ballot initiative in California that cleared a crucial hurdle this month, setting the stage for a probable November vote that could influence not just food packaging but the future of agriculture.
Millions at the ready
Tens of millions of dollars are expected to be spent on the election showdown. It pits consumer groups and the organic food industry, both of which support mandatory labeling, against more conventional farmers, agricultural biotechnology companies, such as Monsanto, and many of the nation's best-known food brands, such as Kellogg's and Kraft.
The heightened stakes have added fuel to a long-simmering debate over the merits of genetically engineered crops, which many scientists and farmers believe could be useful in meeting the world's rapidly expanding food needs.
Supporters of labeling argue consumers have a right to know when food has been modified with genes from another species, which they say is fundamentally different from the selective breeding process used in nearly all foods.
Almost all of the corn and soybeans grown in the United States now contain DNA transferred from bacteria. The foreign gene makes the soybeans resistant to a herbicide used in weed control and causes the corn to produce its own insecticide.
"Makes me nervous"
"It just makes me nervous when you take genetic matter from something else that wouldn't have been done in nature and put it into food," said LaPier, 44, a mental health counselor whose guerrilla labeling was inspired by the group Label It Yourself.
She worries that her daughter, 5, could one day suffer ill effects, such as allergies.
The FDA has maintained that labeling is generally not necessary because the genetic modification does not materially change the food.
Farmers, food and biotech companies and scientists say labels might lead consumers to reject genetically modified food -- and the technology that created it -- without understanding its environmental and economic benefits.
A national science advisory organization recently termed those benefits "substantial," noting existing biotech crops have for years let farmers spray fewer or less harmful chemicals -- although the emergence of resistant weeds and insects threatens to blunt that effect.