The argument over genetically modified food has been dominated, in recent years, by a debate over food labels — specifically, whether those labels should reveal the presence of GMOs.

The battle, until now, has gone state by state. California refused to pass a labeling initiative, but Maine, Connecticut and Vermont have now passed laws in favor of GMO labeling.

Opponents of GMO labeling, including some of the biggest food manufacturers, have turned to Congress, and this week they achieved their first notable success.

A solid majority of the House of Representatives on Thursday voted in favor of a law that would block states from mandating GMO labels.

The debate in Congress followed familiar lines. Opponents of the bill, such as Rep. Chellie Pingree, a Democrat from Maine who is also an organic farmer, argued that it's important for consumers to know what they are eating.

Food labels, she pointed out, already tell consumers many things.

"We know how many calories are in it, thanks to the labels. We know how much vitamin C we get per serving. We know if a fish is farm-raised or wild-caught, and we want to know those things. Shouldn't we also be able to know if the food we are buying has GMO ingredients?" she asked.

Opponents of the bill called it an infringement of the public's right to know what's in their food.

Congressional supporters of the bill, meanwhile, argued that mandating labels on foods containing GMOs actually is misleading, because it suggests to consumers that GMOs are somehow risky to eat — which they are not, according to the Food and Drug Administration.

"Mandatory labeling of genetically engineered products has no basis in legitimate health or safety concerns, but is a naked attempt to impose the preferences of a small segment of the populace on the rest of us," said Republican Rep. Mike Pompeo of Kansas, the bill's primary sponsor.

Supporters of the bill also argued that mandatory labels would raise the cost of food.

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