A coalition of environmental groups is challenging a conservation plan proposed by Central Maine Power as part of its permit to develop a new electric transmission line through western Maine.

The groups filed an appeal with Maine’s Board of Environmental Protection asking regulators to require CMP to protect more mature forest habitat.

“The transmission line has already caused harm by fragmenting mature forest habitat,” said Natural Resources Council of Maine woods, waters and wildlife director Luke Frankel in a press release.

“We’re calling on the BEP to ensure that CMP’s conservation plan complies with the requirements in the permit,” Frankel said.

The council was joined in the appeal by Maine Audubon, Appalachian Mountain Club and Trout Unlimited.

Central Maine Power was required to set aside 50,000 acres of forest in exchange for building the new transmission line to connect Quebec hydropower to the New England electric grid. The company’s plan was approved by the Maine Department of Environmental Protection earlier this year.

But the conservation groups said that instead of selecting forest with older, taller trees, CMP proposed to preserve tracts of heavily-logged timberland that could be harvested in the future. The plan doesn’t meet the state’s requirements to conserve mature forest as a condition of CMP’s development permit, they argue.

The groups want the board to make CMP change the plan and purchase an additional 10,000 acres of older forest.

The appeal is not intended to block or delay completion of the power corridor, according to the groups. The corridor was the focus of years of political and legal battles.

The power line is expected to come online by the end of 2025. A CMP spokesperson did not immediately respond to a request for comment.