Supporters and producers of organic foods petitioned the US government Tuesday for mandatory labeling of genetically engineered foods, and encouraged consumers to go online and join the cause.

The 21 petitioners want the Food and Drug Administration (FDA) to use the full power of the law to ensure that consumers know when they are buying food made with genetically modified ingredients.

"The absence of mandatory labeling disclosures for genetically engineered foods is misleading to consumers," says the 25-page legal petition, drafted by lawyers at the non-profit Center for Food Safety in Washington.

"The requested actions are necessary to prevent economic fraud, and to protect consumers who are deceived by thinking the absence of labeling means the absence of genetically engineered foods."

To pile on the pressure, organizers launched a website, justlabelit.org, on Tuesday where the American public can "flood" the FDA with a pre-written comment in support of the petition.

"Genetically engineered foods are required to be labeled in the 15 European Union nations, Russia, Japan, China, Australia, New Zealand, and many other countries around the world," the prepared comment says.

"As an American, I firmly believe I should also have the right to know if my foods have been genetically engineered."

Not part of the petition effort, but echoing its message, is a 16-day march from New York to Washington via Philadelphia and Baltimore that is calling for "genuine transparency" and labeling for genetically engineered foods.

It aims to reach the gates of the White House on October 16.

The quest for labeling is likely to be resisted by big names in the biotech industry, including Monsanto. It scored points in Europe last month when the European Court of Justice ruled that EU member states must notify Brussels before banning genetically modified crops.

Ken Cook, executive director of the Environmental Working Group, a non-profit group that put its name to the petition, told AFP there is overwhelming public support for labeling genetically engineered foods.

"Most of the polls I've seen are 80 to 90 percent and above in favor of labeling," Cook said Tuesday. "There is tremendous public support and it is time to focus (that support) on the FDA."

"The founding principle of the United States is that the consumer is always right," he added, stressing that campaigners are not demanding an outright ban on genetically engineered food.

Producers of organic meat, chicken, dairy products and seeds, and their industry associations including the Vermont-based Organic Trade Association, make up the majority of petitioners.

"These companies are of the view that they can produce very high quality food" without using genetically altered ingredients, Cook said. "There is an economic interest here, but we see this as another way to 'green' the economy."

Responding to questions by email, an FDA spokeswoman told AFP that the agency had not yet "officially" received the petition, but that it expected to do so "shortly."

"Foods derived from genetically engineered plants must meet the same safety and legal standards as foods derived from their non-genetically engineered counterparts," she added.

"Producers and manufacturers are free to include information in product labeling indicating whether their product is or is not produced using genetic engineering, so long as the information is truthful and not misleading."