GREAT BARRINGTON, Mass. — On a recent sunny morning at the Big Y grocery here, Cynthia LaPier parked her cart in the cereal aisle. 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 GMO’s (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.
Labeling bills have been proposed in more than a dozen states over the last 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 American agriculture.
Tens of millions of dollars are expected to be spent on the election showdown. It pits consumer groups and the organic foodindustry, both of which support mandatory labeling, against more conventional farmers, agricultural biotechnology companies like Monsanto and many of the nation’s best-known food brands like 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 that 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 crops.
Almost all the corn and soybeans grown in the United States now contain DNA derived from bacteria. The foreign gene makes the soybeans resistant to an herbicide used in weed control, and causes the corn to produce its own insecticide.
“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 Ms. 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 like allergies.
The F.D.A. has said that labeling is generally not necessary because the genetic modification does not materially change the food.
Farmers, food and biotech companies and scientists say that 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 in 2010 termed those benefits “substantial,” noting that existing biotech crops have for years let farmers spray fewer or less harmful chemicals, though the emergence of resistant weeds and insects threatens to blunt that effect.
In a letter circulating on social networks, one Iowa farmer, Tim Burrack, criticized this month’s O, the Oprah Magazine, whichcited research linking genetic engineering to health concerns that many scientists have discredited and proposed “5 Ways to Lessen Your Exposure to GMO’s.” Mr. Burrack urged Ms. Winfrey not to “demonize GM crops.”
But some food experts argue that food manufacturers have an obligation to label. Consumers “have a right to take genetic modification into consideration,” said Marion Nestle, a professor of nutrition, food studies and public health at New York University. “And if the companies think consumer objections are stupid and irrational, they should explain the benefits of their products.”
Until now, Americans have made little fuss about genetically modified crops on the market compared with Europeans, who require that such foods be labeled. Demonstrators in Britain are threatening to destroy some genetically modified wheat being grown in a research trial near London.
The current push for labeling in this country stems in part from a broadening of the genetically modified menu to include herbicide-resistant alfalfa and the possible approval this year of a fast-growing salmon, which would be the first genetically engineered animal in the food supply.
Gary Hirshberg, chairman of Stonyfield Farms, the organic yogurt company, has raised more than $1 million for the Just Label Itcampaign to influence the F.D.A. after fighting approval of engineered alfalfa, arguing that cross-pollination would contaminate organic crops fed to cows.
“This is an issue of transparency, truth and trust in the food system,” Mr. Hirshberg said.
Biotechnology companies say that the California labeling initiative, while portrayed as promoting consumer choice, is really an effort by some consumer and environmental groups and organic food growers to drive genetically modified foods off the market.
“These folks are trying to use politics to do what they can’t accomplish at the supermarket, which is increase market share,” said Cathleen Enright, an executive vice president at the Biotechnology Industry Organization, which represents Monsanto and DuPont.
Rather than label food with what consumers might regard as a skull and crossbones, the companies say food producers may ultimately switch to ingredients that are not genetically modified, as they did in Europe.
If the California initiative passes, “we will be on our way to getting GE-tainted foods out of our nation’s food supply for good,” Ronnie Cummins, director of the Organic Consumers Association, wrote in an letter in March seeking donations for the California ballot initiative. “If a company like Kellogg’s has to print a label stating that their famous Corn Flakes have been genetically engineered, it will be the kiss of death for their iconic brand in California — the eighth-largest economy in the world — and everywhere else.”
The Grocery Manufacturers Association, which represents major food brands, declined to comment on what members would do if the California measure passed. But Rick Tolman, chief executive of the National Corn Growers Association, said after meeting with food executives this month that he had the “strong impression” that they would rather reformulate their ingredients than label their products genetically engineered. “They think a label will undermine their brand,” he said.
When asked if they wanted genetically engineered foods to be labeled, about 9 in 10 Americans said that they did, according to a 2010 Thomson Reuters-NPR poll.
The current call for transparency has resonated among some Americans upset by reports of BPA (a chemical used in plastics) in food packaging and pink slime (an ammonia-treated additive) in meat. Ms. LaPier has made an effort to label Kashi cereals, which advertise themselves as natural, since learning they contain genetically modified soy. Since discovering the Label It Yourself Facebook page in March, she has added several of her own pictures to its gallery of handmade labels on grocery store shelves across the nation.
Depending on the jurisdiction, such labeling could constitute a trademark violation against the manufacturer or a trespass against the store. No one has been prosecuted, but also, no one has been caught, according to a spokesman for the group.
So far, the F.D.A. has said only that it is studying the labeling petition; none of the state-level labeling bills proposed over the last year have passed.
For labeling proponents, California, where the Legislature would be bypassed by a direct popular vote, is the big prize.
A decade ago in Oregon, a similar measure that appeared to have the support of two-thirds of voters was rejected after a last-minute spending blitz by labeling opponents. With the financial backing of the organic industry, labeling supporters in California say they will be better prepared.