American Electric Power maintains it never violated federal Clean Air rules to cut pollution.
Even so, the Columbus-based power company has agreed to pay at least $4.6 billion to reduce chemical emissions blamed for spreading smog and acid rain across a dozen eastern states.
The government calls it the nation's largest environmental settlement, and it ends an eight-year legal battle.
AEP says it already has spent or was planning to spend $5.1 billion on scrubbers and other equipment to clean up its smokestack pollution.
Assistant U.S. Attorney General Ron Tenpas says there's a big difference between a company saying it plans to do something and a company being bound by a court order to take those steps.