A sign protesting the proposed Central Maine Power corridor is seen on a mailbox on the side of a road in The Forks on Aug. 20. Credit: Natalie Williams / BDN

Three conservation groups are asking a judge to stop construction of a 145-mile power transmission line corridor to bring Canadian hydropower to the New England grid.

The request for a preliminary injunction was filed late Wednesday by the Sierra Club, Natural Resources Council of Maine and Appalachian Mountain Club, three groups already suing for a more extensive environmental review by the Army Corps of Engineers.

There’s urgency because Central Maine Power’s corporate parent announced construction would begin “in the coming weeks” after the Army Corps last week granted the final permit for work to begin. “It is not in the best interests of Maine people for CMP to start work prematurely on what is one of the most consequential and controversial projects in recent history,” the conservation groups said in a statement.

The $1 billion New England Clean Energy Connect would provide a conduit for up to 1,200 megawatts of Canadian hydropower to reach the regional power grid, reducing greenhouse emissions and stabilizing energy costs, supporters say. Critics, however, have said the benefits are overstated, and that the project would destroy unspoiled wilderness.

The project previously received approval from the Maine Department of Environmental Protection, Maine Land Use Planning Commission and Maine Public Utilities Commission.

The project’s backers also must obtain a so-called “presidential permit” issued by the Department of Energy for the cross-border connection, but that’s not seen as a significant hurdle, officials said.

Opponents already sued in federal court to force the Army Corps to conduct a more rigorous environmental impact statement instead of the less-stringent environmental assessment.

The project, which would be fully funded by Massachusetts ratepayers to meet the state’s clean energy goals, calls for construction of a high-voltage power line from Mount Beattie Township on the Canadian border to the regional power grid in Lewiston.

Much of the project calls for widening existing corridors, but a new swath would be cut through 53 miles of wilderness. It would cross the Appalachian Trail and several hundred wetlands and streams, according to the Natural Resources Council of Maine.

Story by David Sharp.