A coalition of a dozen national and Midwestern agricultural groups sued on Wednesday to overturn a California decision that could force the popular weed-killer Roundup to carry warning labels that it can cause cancer.

The lawsuit filed in federal court in Sacramento seeks an injunction barring the state from enforcing what the suit describes as a "false" and "misleading" warning.

It claims California's decision violates constitutional due-process and free-speech rights and should be superseded by federal regulations.

Roundup's main ingredient, glyphosate, is not restricted by the U.S. Environmental Protection Agency, and has been used widely since 1974 to kill weeds while leaving crops and other plants alive.

But the International Agency for Research on Cancer, based in Lyon, France, has classified it as a "probable human carcinogen." That prompted the California Office of Environmental Health Hazard Assessment to add glyphosate this summer to a list of chemicals known to cause cancer. The listing could lead to a requirement for warning labels on the product.

The plaintiffs in the lawsuit include the national wheat and corn growers associations, state agriculture and business organizations in Iowa, Missouri, North Dakota and South Dakota, and a regional group representing herbicide sellers in California, Arizona and Hawaii. The plaintiffs also include St. Louis-based Monsanto Co., which makes Roundup.

The lawsuit contends that California's "false warning" has harmed Monsanto's reputation and its investment of hundreds of millions of dollars in the herbicide and glyphosate-tolerant seeds.

The suit also alleges a ripple-effect on food production across the country. It says entities that process crops for food products sold in California would have to stop using glyphosate-treated crops, add warning labels that could diminish demand for their products or engage in costly tests to show that any glyphosate residue is at safe levels.

California's cancer warning "would result in higher food costs, crushing blows to state and agricultural economies and lost revenue up and down the entire supply chain," Gordon Stoner, president of the National Association of Wheat Growers, said in a written statement.

Sam Delson, a spokesman for the California Office of Environmental Health Hazard Assessment, said the agency hadn't yet reviewed the new filing but is confident its rules are legal.

In March, a California state court judge dismissed a separate lawsuit by Monsanto challenging California's cancer warning.

Midwestern states and interest groups also have challenged other California agricultural policies.

A federal appeals court panel ruled last year that six states — Missouri, Nebraska, Oklahoma, Alabama, Kentucky and Iowa — lacked the legal right to challenge a California law barring the sale of eggs from chickens not raised in accordance with California's roomier cage-space requirements. The U.S. Supreme Court declined this year to hear an appeal.

___

Follow David A. Lieb at: http://twitter.com/DavidALieb