Lawyers for the Neskantaga First Nation say the province may have broken the law by signing deals with Cliffs Natural Resources, before consulting First Nations.
Gregory McDade, with the B.C.-based firm Ratcliff and Company, said that lack of consultation threatens the entire multi-billion-dollar mining project in Ontario's James Bay lowlands.
"It would appear that Ontario is already in breach of their legal duties towards Neskantaga," McDade wrote in a letter to Ontario's mining minister. "It will be difficult for you to reconcile this lack of prior consultation with decisions already apparently made."
The letter comes after announcements last week that Ontario had an "agreement in principle for key elements" of Cliffs' chromite project.
"We ask that Ontario take no further steps to support this project until adequate consultation with my client has been achieved, and until full discussion has been held with northern First Nations towards a proper environmental assessment and regional decision-making forum," McDade wrote in the letter dated May 10.
Ontario's Minister of Aboriginal Affairs, Kathleen Wynne, on Monday said she can't comment on the allegation in the letter, but she wants to move forward now with talks.
"I believe it is critical to the future success to the economy in the North that we get this right," she said.
Neskantaga Chief Peter Moonias said the mining development at the headwaters of the Attawapiskat River could destroy his community.
Moonias said he's afraid to even say hello to a provincial minister because he said the province seems to think any conversation is consultation.
Wynne said the province will continue to do its best to communicate with First Nations.
"If we can work together then all of the children in his community and the other First Nations communities will benefit from this project," she told CBC News.
Meanwhile, Moonias says he won't let Cliffs cross the Attawapiskat River near his community to access its mine site.