A court fight over use of a new Dow Chemical herbicide on genetically engineered U.S. corn and soybean crops is growing to encompass 15 Midwestern states after the company recently won federal approval for more widespread application.

Conservationists, food safety and public-health advocates want to block the use of Enlist Duo until the court can consider its impact on human health, said Paul Achitoff, a public interest lawyer for Earthjustice, representing the plaintiffs.

The coalition's original lawsuit filed in October in the 9th Circuit Court of Appeals challenged a decision by the Environmental Protection Agency to allow Enlist Duo to be used in six states. A motion filed Monday seeks to add nine states where the EPA approved the herbicide for use on April 1.

Enlist Duo's ingredients include 2,4-D, a component of the defoliant Agent Orange widely used by the U.S. military in the Vietnam War. The substance has been linked to Parkinson's disease, non-Hodgkin lymphoma and reproductive problems, said a statement by plaintiff Center for Food Safety.

Achitoff said the coalition expects a ruling any day on its motion for an emergency stay on the use of the herbicide until the lawsuit is decided.

A spokesperson for the EPA did not immediately respond to a request for comment.

The stay motion focuses on what Achitoff said was EPA's failure, prior to registering the herbicide for use, to consult with the U.S. Fish and Wildlife Service on the herbicide's impacts on endangered species including the whooping crane, Louisiana black bear and Indiana bat.

Enlist Duo was designed to be a weed killer on fields planted with special soybean and corn seeds genetically engineered by Dow to be resistant to the herbicide.

The Dow herbicide/seed package is part of a second wave of genetically engineered commercial crops. Most of the original group of genetically engineered seeds, called Roundup Ready, were created in the 1990s to be resistant to Monsanto's Roundup herbicide, according to the center.

Over the past 20 years, however, millions of acres of farmland have become infested with Roundup-resistant super weeds, leading to Dow's new formulation.

The case is Center for Food Safety et al v. U.S. Environmental Protection Agency and intervenor Dow Agrosciences, the U.S. Court of Appeals for the 9th Circuit, No. 14-73359.

For the petitioners: Paul Achitoff and Gregory Cahill Loarie of Earthjustice, Andrew Kimbrell and Sylvia Wu of the Center for Food Safety

For the respondents: John Brett Grosko and T. Monique Peoples of the U.S. Department of Justice; for Dow Agrosciences, Christopher Landau of Kirkland & Ellis and David Weinberg of Wiley Rein