Environmentalists sued the US Forest Service on Tuesday in an attempt to reverse a 2017 land transfer that gave PolyMet Mining more than 2 670 ha needed to build an open pit copper and gold mine in northern Minnesota.

The suit, led by the Center for Biological Diversity (CBD), claims the project would destroy a region home to Canada lynx and northern long-eared bat, both of which are listed as threatened with extinction under the US Endangered Species Act.

"These federal agencies can't just ignore threats to animals headed for extinction," said CBD attorney Marc Fink.

Similar lawsuits from CBD and others failed in 2019, with the court finding the parties lacked standing because PolyMet had not yet obtained permits and thus there was no way to measure if the project would cause imminent harm to the region.

PolyMet has since acquired the land and obtained most of its permits. The environmental groups are asking the court to now hear their claims on the merits and order the Forest Service to take back the land.

The US Fish and Wildlife Service, the US Army Corps of Engineers and US Secretary of the Interior Deb Haaland in her official capacity are co-defendants.

PolyMet, which is controlled by mining giant Glencore , said it believes the land transfer will stand. "We're confident we'll be able to address whatever issues arise," spokesperson Bruce Richardson said.

Other parties joining CBD in the lawsuit include the Save Lake Superior Association, Save Our Sky Blue Waters, Friends of the Cloquet Valley State Forest and Duluth for Clean Water.

The case is Center for Biological Diversity et al v. Deb Haaland, Secretary of the Interior et al, US District Court for the District of Minnesota, No. 0:22-cv-00181.

The lawsuit comes the day after a state court ordered regulators to reconsider a wastewater permit for the PolyMet project.