On Tuesday, voters in Washington state defeated a measure that would have required labels on food containing genetically engineered ingredients.
A similar effort failed in California last year, so now attention turns to roughly two dozen other states - including Pennsylvania and New Jersey - where bills are pending.
"Food labeling is a new political movement that will not go away," said the chair of Washington's campaign, Democratic State Sen. Maralyn Chase. She said that although the measure failed, the campaign was a success because it focused attention on the issue.
Labeling proponents say consumers have a right to know what's in their food.
Opponents say labels suggest that genetically engineered foods are unsafe or inferior, and would lead to higher costs.
Ultimately, the labeling battle comes down to a debate over the technology itself, which involves inserting a specific gene into the DNA of a plant to introduce a new trait, such as herbicide resistance.
According to the industry, 70 percent to 80 percent of the food Americans eat has genetically engineered ingredients - also referred to as GMOs, for genetically modified organisms. Most corn, soybeans, and sugar beets grown in the U.S. are genetically engineered.
Supporters of GMO crops say the technology could ease world hunger and make crops less susceptible to droughts or other effects of climate change. They say genetically engineered crops require fewer pesticides and less work, meaning less fuel consumed by tractors.
Opponents say that the technology has not been independently verified to be safe for humans or for the environment. They also say it gives corporate entities too much control over our food.
In Washington, the anti-labeling side raised $21.4 million, making it the most expensive opposition to a ballot measure in state history.
Top contributors were the Grocery Manufacturer's Association and major biotech firms - Monsanto, DuPont Pioneer, Dow AgroSciences, and Bayer CropScience.
The pro-labeling side raised $6.3 million, much of it coming from Dr. Bronner's Magic All-One, a California-based organic soap maker. The Center for Food Safety, a Washington, D.C. nonprofit also contributed.
Cathy Enright, executive director of the industry's Council for Biotechnology Information, said the vote showed "that talking with consumers about how our food is grown doesn't require a warning label." But it also showed the industry "hasn't done the best job" talking about GMOs. "We have a lot of ground to make up."
Rebecca Spector, West Coast director of the Center for Food Safety, said money swung Tuesday's vote. She said it was hard to counter the "confusing and misleading" industry ads "when you're outspent by 3-to-1."
Bills to require labeling have been introduced in New Jersey's Senate and Assembly, with bipartisan support. Sen. Bob Singer (R., Ocean), said he would seek to align both bills.
A Pennsylvania bill was introduced in the Senate in March, and in the House weeks ago - with nine Republican and 20 Democratic cosponsors.
Sam Bernhardt, Pennsylvania organizer for the pro-labeling Food and Water Watch, said "there's a lot of energy in Pennsylvania on this issue."
GreenSpace: More Information
The website www.GMOAnswers.com is an industry-sponsored resource for consumers, who can engage in Q&As with experts.
The Center for Food Safety, a nonprofit pro-labeling group based in Washington, D.C., also is a resource at www.CenterForFoodSafety.org
The center's tips for avoiding genetically engineered foods include:
Buy organic. Certified organic products are not permitted to have genetically engineered ingredients.
Look for "non-GMO labels." Some food producers are targeting consumers who do not want genetically modified foods as ingredients.
Avoid foods with ingredients that that are likely to be genetially engineered, including corn, soybeans, canola, beet sugar, and cottonseed.
Buy fresh rather than processed foods.
"GreenSpace," about the environment and health, appears every other week, alternating with Art Carey's "Well Being" column.