(Reuters) -- An Italian judge has ordered Tirreno Power, 50 percent-owned by France's GDF Suez SA (EPA:GSZ), to turn off two coal-fired units at its Vado Ligure plant due to environmental concerns, the Italian electricity generator said.

The website of state-owned broadcaster Rai reported that prosecutors in the city of Savona are investigating Tirreno Power for "environmental disaster" and manslaughter, alleging that fumes killed 442 people between 2000 and 2007.    

Italy relies on gas-fired plants and renewable power sources for most of its electricity generation, while coal-fired plants have faced fierce environmental opposition.

The Vado Ligure plant in northern Italy consists of a combined-cycle unit powered by natural gas with a capacity of 800 megawatts and two coal-fired units, each with a capacity of 330 MW that date back to 1971.

"They have shut down the two coal units, while the combined-cycle one is not affected by the measure," a spokesman for Tirreno Power said on Tuesday, adding the ruling seemed to be related to a violation of environmental requirements.

"We do not understand the rational for this decision."

Tirreno Power said in a statement its technical and legal teams were examining the decision and that it would respond in due course, but added that it had always operated in full compliance with the law and done business in a responsible way.

State-controlled Enel SpA (BIT:ENEL), Italy's biggest utility, has been trying for years to convert its big Porto Tolle power plant in the north to coal but has met with stiff resistance.

Enel built Tirreno Power in the 1970s and sold it in 2003 as part of a liberalization package.

The remaining 50 percent of Tirreno Power is controlled by special vehicle Energia Italiana, which is 78 percent owned by Italian energy group Sorgenia, part of holding group CIR.

The rest of Energia Italiana belongs to Italian utilities Iren SpA (BIT:IRE) and Hera SpA (BIT:HER), which hold 11 percent each.