KANSAS CITY, Missouri (Reuters) - Opponents of biotech crops said on Wednesday they were filing a lawsuit to challenge the USDA's deregulation of Monsanto Co's genetically engineered sugar beet because of fears of 'biological contamination' and other harm to the environment.

The Center for Food Safety, the Sierra Club and two organic seed groups said the lawsuit involved the United States Department of Agriculture's approval of Monsanto's glyphosate-resistant sugar beet, which is engineered to withstand treatment of Monsanto's Roundup herbicide.

The 'Roundup Ready' sugar beets are slated to be grown on a commercial scale for the first time in the United States this year, the groups said.

Neither Monsanto nor USDA officials could be reached immediately for comment.

The groups said the wind-pollinated biotech sugar beets will cross-pollinate and contaminate conventional sugar beets, organic chard and table beet crops.

As well, the groups said the biotech sugar beets will increase the recent rise of weeds resistant to herbicide, which have been reported on 2.4 million acres of U.S. cropland, the groups said.

'The law requires the government to take a hard look at the impact that deregulating Roundup Ready sugar beets will have on human health, agriculture and the environment,' said Greg Loarie, an attorney at the Earthjustice law firm, which is helping represent the plaintiffs. 'The government cannot simply ignore the fact that deregulation will harm organic farmers and consumers, and exacerbate the growing epidemic of herbicide-resistant weeds.'

The lawsuit is similar to one biotech crop opponents filed over the USDA's deregulation of Monsanto's genetically altered alfalfa, which led a federal judge last year to issue a nationwide ban against the planting of the Roundup Ready alfalfa.

The judge found that U.S. regulators improperly allowed the commercialization of the biotech alfalfa without a thorough examination of its effects.

(Reporting by Carey Gillam, editing by Jackie Frank)