The Sierra Club has filed an intent-to-sue notice against Minnesota Power, alleging violations of soot standards at three coal-fired power plants in northeastern Minnesota.
The environmental group says the utility's own data show its Boswell, Taconite Harbor, and Laskin plants have violated standards for particulate emissions more than 10,000 times over the last five years.
The Sierra Club also alleges Minnesota Power has violated various other permit requirements related to its operation of pollution control equipment hundreds of times since 2009.
Federal law allows citizens to file lawsuits alleging violations of the Clean Air Act with 60 days advance warning.
Organizer Michelle Rosier says they're calling on Minnesota Power to commit itself to replacing the coal-fired plants.
Minnesota Power officials dispute the Sierra Club's claims and defend their environmental record.