US farmers joined with the food industry Thursday to launch a united front against labeling genetically modified products, amid mounting consumer pressure and an ongoing trade dispute with China.

More than half of US states introduced bills aimed at requiring GMO labeling last year, in a country where 80 percent of the food contains ingredients that were made with genetically modified organisms.

While only two states have passed such measures, and none have yet implemented any labeling requirements, farmers are clearly concerned about the prospect.

"If each state had a different label requirement, our farmers just couldn't adapt to that and really economically grow safe, affordable food," said Ray Gaesser, president of the American Soybean Association which represents 600,000 US farmers.

Gaesser estimated that any new state-by-state labeling laws would hike prices 15 to 30 percent.

Stressing the lack of scientific evidence that GMOs cause harm, Gaesser joined with corn farmers, bakers, restaurants, fisheries, animal feed and grocery store groups in forming the 30-member Coalition for Safe Affordable Food.

The umbrella group aims to "avoid unnecessary and confusing 50-state patchwork of GMO labeling laws," said Pamela Bailey, president and CEO of the Grocery Manufacturers Association.

Instead, members are calling for a federal solution that would only mandate GMO labeling "if the FDA, our nation's foremost food safety authority, determines that there is a health or safety risk," she told reporters.

"Up until now, (the) FDA has said GMO technology is safe and it would be misleading to mandate a label on a GM product," Bailey said.

Recognizing that some consumers want to know more about what is in the foods they eat, Bailey asked the FDA "to outline clear labeling standards that companies can use voluntarily."

Corn, soybeans and sugar beets have been genetically modified in the United States for many years, and farmers say these altered seeds are more resilient against pests and harsh weather.

Wheat is the only major crop that has not gained approval for genetic modification, as the prospect of GMO wheat faces resistance from foreign exporters, particularly in Asia.

When it comes to corn, which is typically accepted abroad in GMO form, an ongoing dispute with China remains unresolved and is dampening global trade.

China has blocked or cancelled hundreds of thousands of tons of a certain strain of GMO corn produced in the United States since late last year, according to the US Department of Agriculture.

"If there was any indication that GMO ingredients were not safe, we would not be using them," said Martin Barbre president of the National Corn Growers.

"Obviously there is a little issue with China now as we speak but we are working to get that resolved."

Consumer pressure in the United States is a key driver of state ballot initiatives that aim to label GMO foods, and health advocacy groups like the Center for Food Safety have said to expect more in the year ahead.

California narrowly rejected a 2012 initiative to require GMO labeling, which was fought with tens of millions of dollars in advertising from corporate giants like DuPont, Monsanto, Syngenta, Kraft, Coca-Cola and Pepsi.

Only Maine and Connecticut have approved GMO labeling measures, though no changes have come into effect because the laws require several contiguous states to first adopt similar labeling requirements.

GMO technology "has been used safely in our food supply for 20 years," said Bailey.

"Efforts to label these foods otherwise are often the product of misinformation."