Supreme Court justices on Tuesday sharply questioned a lower court's decision that has prohibited biotech giant Monsanto Co. from selling genetically engineered alfalfa seeds, possibly paving the way for the company to distribute the seeds for the first time since 2007.

The case has been closely watched by environmentalists and agribusiness. A federal judge in San Francisco barred the planting of genetically engineered alfalfa nationwide until the government could adequately study the crop's potential impact on organic and conventional varieties.

St. Louis-based Monsanto is arguing that the ban was too broad and was based on the assumption that their products were harmful. Opponents of the use of genetically engineered seeds say they can contaminate conventional crops, but Monsanto says such cross-pollination is unlikely.

Organic groups and farmers exporting to Europe, where genetically modified crops are unpopular, have staunchly opposed the development of such seeds.

Environmentalists are concerned with the case's effect on a federal law that requires the government to review a product's effect on the environment before approving it. The U.S. Agriculture Department earlier approved the seeds, but courts in California and Oregon said USDA did not look hard enough at whether the seeds would eventually share their genes with other crops.