HELENA, Mont. (AP) — An environmental group is suing Montana environmental regulators over a permit allowing the expansion of a gold mining operation near Whitehall without requiring the Canadian company to completely backfill the new open pit after the mining ends.

The reclamation plan approved by the state Department of Environmental Quality in its operating permit to Barrick Gold Corp. violates the Montana Constitution’s right to a clean and healthful environment, the Montana Environmental Information Center claimed in its lawsuit filed Monday.