Experts and industry groups say such an injunction could jeopardize U.S. sugar supplies, about half of which comes from the biotech beets planted on more than 1 million acres in 10 states stretching from Michigan to Oregon.
"It will be a big problem," if the injunction is granted, said Carol Mallory-Smith, professor of weed science at Oregon State University. "The industry really had converted to this."
The beets, engineered to be resistant to Monsanto's popular herbicide Roundup, comprise 95 percent of the crop after two seasons of planting. All the seed comes from Oregon's Willamette Valley.
Organic farmers, food safety advocates and conservation groups already have won a lawsuit forcing federal authorities to reconsider their 2005 approval of the Roundup Ready beets for unrestricted use, saying the government failed to take a hard look at cross-pollination risks.
If granted at a hearing scheduled for Friday in San Francisco, a requested injunction would halt planting of the altered beets until the U.S. Department of Agriculture's Animal and Plant Health Inspection Service does an environmental impact statement - a process that could take two or three years.
The farmers also want to bar the sale of any sugar made from genetically engineered beets.
"The sugar beets were unlawfully deregulated," said Paul Achitoff, an attorney for Earthjustice, the environmental public interest law firm representing plaintiffs. "The court has already found that. Legally, they shouldn't be on the market.
"Consumers should not be exposed to it," he said. "The environment should not be exposed to it."
In 2007, another lawsuit stopped planting of Roundup Ready alfalfa pending an environmental review, though at that point only a small percentage of farmers used it. The U.S. Supreme Court will hear Monsanto's appeal.
The latest lawsuit's roots are in Frank Morton's small farm outside the small town of Philomath on the western edge of the Willamette Valley, where he grows seed for organic vegetables in fields surrounded by tall trees.
When he learned BetaSeed in nearby Tangent and other growers were producing genetically modified sugar beet seed for use elsewhere, he went to his local growers' association and tried to get them to push back.
"They told me if you don't like it you can sue USDA. So we did," he told The Associated Press last September. He has since stopped talking about the case.
The problem is not just the potential for cross pollination. Testing is so sensitive now that genetically engineered pollen could be detected on his crops, making them worthless, whether it pollinates them or not, Morton said.
The Center for Food Safety and the Organic Seed Alliance also worry Roundup Ready crops - which include corn, soybeans and cotton - are creating herbicide-resistant weeds and threaten food safety.
Sugar beet growers declined interview requests, referring questions to the American Sugar Beet Growers Association. Spokesman Luther Markwart characterized the injunction request as "radical."
"It would have disastrous impacts on the 10,000 growers, our processors, the seed companies, and the economies of 10 states," he said.
If the groups believed there was an immediate threat, he said, they should have filed for an injunction two years ago rather than wait until the biotech beets were being "widely and safely used," he added.
Agricultural extension educator Jim Gill in Worland, Wyo., said they are worried about the case, and already have invested in preparing for this year's crop. Planting starts in early April in the Big Horn Valley.
If the injunction is granted, there is not enough conventional seed and related herbicides to go around, and farmers will have to scramble to plant other crops, he said.
"It's a tough situation. There's a lot of money that's already been invested - put in the ground - to prepare for the 2010 crop," he said. "These are all things that these guys and gals are trying to figure out."
The court hearing will focus on whether allowing this year's crop to be planted is likely to cause irreparable harm.
Mallory-Smith said growers already take precautions to prevent cross-pollination between conventional crops, and the Roundup Ready seed growers are keeping their distance from Morton's farm.
Monsanto spokesman Garrett Kasper said the past two years have demonstrated the beets are safe.
Achitoff counters that there's already evidence in the ground in Oregon that growers are not heeding the precautions.
Last May, specklings - tiny roots planted to produce seed - for Roundup Ready sugar beets were found in a batch of compost being sold at a garden center in nearby Corvallis.
"People have these Roundup Ready sugar beets sprouting, whether they are in backyard farms or gardens," he said.
By JEFF BARNARD Associated Press Writer