The federal lawsuit filed Tuesday in Charleston seeks an order barring Bayer from using or producing the chemical at the plant until several conditions are met. Bayer announced in January that it planned to resume using MIC at Institute until mid-2012 when stores are consumed.
Bayer had no immediate comment on the lawsuit.
Among other things, the plaintiffs want Bayer to show it's complied with safety improvements recommended after an August 2008 explosion that killed two plant workers.
That explosion involved different chemicals, but the lawsuit compares it with the MIC leak that killed thousands of people in Bhopal, India, in 1984.
"To Plaintiffs' knowledge, the new process for MIC at Bayer's current facility has never been employed at any location in the United States, or anywhere else; it's startup is, for all practical purposes, an uncontrolled experiment being conducted in a major population center in which 300,000 citizens reside," the lawsuit said.
Bayer said it has spent $25 million on new production, safety and communications equipment ahead of the restart. The company also said it has eliminated all aboveground storage and reduced MIC stocks by 80 percent.
Bayer said it's retrained workers and established several new safety and communications processes with government safety agencies
"All of these efforts -- as well as numerous process and safety reviews along the way, including one recently completed by third-party experts -- have led to our assurance of a safe operation," the company said.
The complaint largely focuses on a report issued by the U.S. Chemical Safety Board in January.
The plaintiffs want Bayer to prove to the court that it and various regulators have complied with the report's recommendations. The reports advised Bayer to improve training its fire brigade and install better pollution monitors and suggested the West Virginia Department of Health and Human Resources start a hazardous chemical release prevention program.
The plaintiffs also want government regulators to inspect the plant and for Bayer to wait until the National Academy of Sciences finishes a congressionally mandated study of the safety issues posed by producing MIC in a major population center. Panel members were announced in January.
The planned resumption mirrors the events that led up to the 2008 explosion, plaintiff Maya Nye said in a document filed with the lawsuit. The restart "presents an unreasonable risk," Nye said.