Representative Mike Pompeo of Kansas introduced legislation aimed at blocking mandatory GMO foods labeling. The "Safe and Accurate Food Labeling Act" would override mandatory labeling legislation that has been introduced in around two dozen states.

"We've got a number of states that are attempting to put together a patchwork quilt of food labeling requirements with respect to genetic modification of foods," says Pompeo. "That makes it enormously difficult to operate a food system. Some of the campaigns in some of these states aren't really to inform consumers but rather aimed at scaring them. What this bill attempts to do is set a standard."

Labeling proponents say consumers should know if foods they are buying contain bioengineered ingredients.