Thousands of acres of publicly-owned, roadless Colorado forests face renewed threat on Monday after the U.S. Forest Service moved to reinstate a loophole that allows major coal companies to bulldoze over protected lands, paving the way for coal mine expansion and increased carbon emissions of the ‘dirtiest’ variety.

“The coal mine loophole is a lose-lose-lose proposition: it’s bad for wildlife, bad for hikers and hunters who enjoy Colorado’s wild forests, and it’s bad for our climate,” said Ted Zukoski, an attorney with the group Earthjustice, which is among the local and national conservation groups sounding the alarm over the rule change.

Known as the North Fork Coal Mining Area exception of the Colorado Roadless Rule, the loophole was rejected last year by the U.S. District Court of Colorado, which ruled that the Forest Service’s approval of Arch Coal’s Environmental Impact Statement failed to consider the climate change impacts of expanding coal mining and burning. The court’s ruling left the door open for the Forest Service to revive the loophole if the agency undertook a new analysis.

According to a Forest Service memo (pdf), the proposed exception would allow for “temporary road construction for coal exploration and/or coal-related surface activities in a 19,100-acre area.” Environmentalists warn that the change will give Arch Coal and other mining companies access to as much as 350 million tons of federal coal, which could result in more than half a billion tons of carbon pollution from mining and burning the coal.

Among the lands threatened by the proposal is the Sunset Roadless Area, which includes lush aspen and spruce-fir forests and abuts the federally-recognized West Elk Wilderness.