The organization, which represents more than 5 million U.S. farmers, called on Bush to "take immediate action" to initiate a WTO complaint against the EU.

The WTO has ruled illegal the EU's 4-year-old moratorium on new biotech products.

While the European Commission has been trying to lift that ban, it is meeting resistance from some member countries.

Earlier this week, the incoming chairman of the Senate Finance Committee, Sen. Charles Grassley of Iowa, also urged the Bush administration to launch a legal case against the EU.

Stallman said the EU's moratorium has resulted in millions of dollars in lost sales for U.S. farmers, including corn growers.

About 70 percent of U.S. soybeans and a quarter of the U.S. corn crop is grown from genetically-modified seeds.

The farm group's letter came just one month after the organization joined with 25 other U.S. agriculture groups urging U.S. Trade Representative Robert Zoellick to file a WTO complaint.

While some key Bush administration officials favor filing the case, the decision was awaiting consideration by Bush's Cabinet, according to sources.

On Monday, David Hegwood, special trade adviser to the U.S. Department of Agriculture, noted the urgency in getting the EU moratorium lifted. But he also left open the possibility of a case not being filed.

"If we can get the moratorium lifted without taking a case, then it saves us a whole lot of time and trouble. But that's our ultimate objective, to get the moratorium lifted," Hegwood told reporters.

Hegwood also noted that filing a WTO complaint could have an impact on other U.S.-EU trade disputes and could create a backlash against biotech foods by European consumers.