OKLAHOMA CITY (AP) — An environmental organization is criticizing an Oklahoma utility's request to increase rates after spending more than $600 million on equipment designed to reduce emissions.

The Oklahoma Gas & Electric Company is updating coal-fired units at the Sooner Power Plant and the Muskogee Power Plant to comply with federal regulations. The company said it kept customer rates 31 percent below the national average while doing work on both plants but is now seeking a nearly $78 million annual rate increase to "recover its investment."

The typical residential customer would see a $7.60 monthly increase, according to the company.

"Due in large part to the actions we've taken at these facilities, overall plant emissions are expected to be significantly lower from 2005 levels," OG&E spokesman Brian Alford said.

The Oklahoma Corporation Commission is considering the request.

The Oklahoma Sierra Club has criticized the move, noting that the company's plans to update the Sooner plant were twice denied approval in recent years by the commission and the courts.

"We are disappointed by OG&E and we strongly object to their request to collect half a billion dollars through higher electric rates on Oklahoma families," said Johnson Grimm-Bridgwater, chapter director of Sierra Club Oklahoma.

The nonprofit also criticized the utility for purchasing an additional coal-power plant instead of seeking cleaner energy options.

"Rather than modernizing and locking in significant amounts of low cost wind and solar like utilities in neighboring states, OG&E continues coming back again and again to the commission asking for a bailout of their old polluting coal plant," Johnson said.