Last year $2.4 billion worth of products were sold with a label saying they do not contain ingredients from genetically modified organisms, but the claim wasn't backed by any government regulatory agency.
Instead, it came from the Non-GMO Project, a nonprofit organization that offers third-party verification that food products are not genetically modified.
Unlike items labeled organic, non-GMO products do not receive endorsement from the Department of Agriculture or the Food and Drug Administration. Those regulators have specific criteria for organic products, and consumers know that any food with an organic label has met those standards.
Brands such as Silk, Kashi and Simply Soy Yogurt have turned to the GMO Project for support to tout their products as non-GMO.
"Consumers want non-GMO choices, so we are working with food companies and retailers to make sure that [these options are] available," said Megan Westgate, executive director of the Non-GMO Project. "Our efforts do not hinge on government regulations or decisions about whether or not to label."
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Natural food retailers started the Non-GMO Project, according to Westgate.
"They were getting a lot of questions from shoppers about how to avoid GMOs. It became clear that in the absence of mandatory labeling we needed to have a third-party verification system," she said.
Since 2008 the organization has supplied a verification mark for products that have undergone its review process. More than 500 brands carry the Non-GMO seal.
The process of earning the label is rigorous, and ongoing testing is required for all ingredients that are at high risk of GMO contamination, Westgate said.
Craig Shiesley, senior vice president of plant-based food and beverages at WhiteWave, said his company's Silk brand earned the Non-GMO Project's label in 2011, but started the transition in 2010.
"For us, one of the underpinnings of being natural is being non-genetically modified," Shiesley said. "It's hard for you to call your product natural if your [product is] not non-GMO."
The entire health and wellness food industry should have transparent labeling, Shiesley said.
"To me this is not just a competitive advantage. I'm hoping the whole industry elevates toward this standard. Regardless of what the scientific the data says, we know that our consumer wants their food wholesome, whole, not genetically engineered," Shiesley said.
"It's a very fundamental right to know what's in the food we're eating and feeding our families, and our label is the fastest-growing label in the natural market," Westgate said.
Others are lobbying the FDA to step in. The "Just Label it Campaign" has petitioned the agency to require labeling of products containing GM ingredients.
"They have collected almost 1.3 million signatures—more than two times the number of signatures the FDA has ever received for any other food-related petition. ... It's a clear indication that Americans want this information," Westgate said.
Currently, the FDA says food manufacturers may indicate through voluntary labeling whether foods have or have not been developed through genetic engineering, provided that such labeling is truthful and not misleading.
"We recognize and appreciate the strong interest that many consumers have in knowing whether a food was produced using genetic engineering," said FDA spokeswoman Theresa Eisenman.
GMOs are banned or labeled in more than 60 countries. Last week, Connecticut became the first state to pass a bill requiring producers to label items sold there containing GM ingredients. The catch: The legislation will go into effect only if other states decide to do the same.
It's unclear if other states will follow suit, but many major consumer package goods companies have lobbied against mandatory GMO labeling.
The Grocery Manufacturers Association, which represents the interest of PepsiCo, General Mills, Kellogg and several other CPG companies opposing mandatory labeling, has also lobbied against such legislation.
Their position is that mandatory labeling will lead to an increase in grocery prices and mislead consumers to believe there is something inherently wrong with genetically modified products.
"The use of genetically modified foods and ingredients is safe," said Brian Kennedy, a spokesperson for the association. "According to a number of U.S. regulatory agencies that study and monitor the topic, including the FDA, there are no health risks associated with the use of genetically modified foods and ingredients."
Many natural food advocates and consumers who oppose the use of GM ingredients in products believe consuming them may have detrimental long-term effects, which Kennedy disputed.
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"All GM technology does is add desirable traits from one plant to another, without introducing anything unnatural or using chemicals, so crops grow quicker, are more plentiful ... They are more nutritious, require fewer pesticides, help foods have a longer shelf life and keep production costs down; they ultimately lower costs to consumers by about 20 to 30 percent," he said.
But opponents want to avoid them. Westgate said the recent discovery of mystery wheat in Oregon is a perfect example of why GM products aren't safe.
"When GMOs are grown out in the environment, contamination happens and it's not possible to control it. That's a real liability to our food supply because these are experimental organisms [and] we don't know what the long-term impact is to human health or the environment," Westgate said.
While the debate goes on, some say, labeling at least provides consumers with information to make a decision. The Non-GMO Project, and other efforts like it, may wind up creating a standard within the industry.
—By CNBC's Karma Allen. Follow him on Twitter