Two groups representing Inuit and Metis members in Labrador are challenging a key part of the development now under construction on the lower Churchill River.
The Nunatsiavut (noon-AHT'-see-ah-voot) Government and the NunatuKavut (noon-ah-TWO'-ha-voot) Community Council have each filed requests for judicial review in Halifax.
They're asking the Federal Court to revisit a decision by the Department of Fisheries and Oceans to grant permission for the dam, which they say was done without proper consultation.
Nunatsiavut president Sarah Leo says the $7.7-billion project will damage recognized Inuit lands and cause potential health issues.
She says concerns about mercury levels were recognized by a federal-provincial environmental assessment panel but have not been acted on.
NunatuKavut president Todd Russell, whose group has no federally recognized land claim, says the province has failed to adequately consult his members.
Authorization to start building the dam was granted to Nalcor Energy, which says it's still reviewing the separate court applications.
Nalcor vice-president Gilbert Bennett, in charge of the Muskrat Falls project, says Ottawa and the province carefully weighed any effects before releasing it from environmental assessment.