In New York, over CO2 regulation.  From Green Hell, WAR! Utility sues New York over CO2 regulation

Indeck Corinth L.P., which operates the Corinth Generating Station, an electric power plant in Corinth, NY, sued New York state on January 29, 2009 claiming that the Regional Greenhouse Gas Initiative (RGGI) that aims to reduce greenhouse gas emissions in the Northeast U.S. is illegal.

More, including a link to the complaint, at Green Hell Blog.

Hope this is just the beginning.