For the first time in its oversight of Baffinland's Mary River project, the Nunavut Planning Commission has found the mining company's plans do not conform with the territory's land use plan.
Baffinland wants to triple the amount of ore shipped from Milne Inlet on northern Baffin Island to 12 million tonnes per year.
That would mean shipping ore from the site 10 months of the year instead of only during the summer, requiring icebreakers travelling through what the commission calls essential areas.
Hunter Tootoo, the commission's chair, says Baffinland's new plan would require ice breaking from Milne Inlet through Eclipse Sound in front of Pond Inlet, all the way out to Baffin Bay.
"In the plan there's essential areas which are harvesting areas and community transportation routes," said Tootoo.
"This ice-breaking disrupts that."
The commission says Baffinland can still move about two-thirds of its ore during the previously-agreed period of June to October.
Baffinland can apply for an exemption or revise its project plans.
Tootoo says the commission's decision was not a simple one.
"Believe me, it was many hours and many days of hard work."