MINNEAPOLIS (AP) -- The proposed PolyMet copper-nickel mine in northern Minnesota has encountered a setback; the state Court of Appeals has ordered regulators to revisit a critical air emissions permit given to the project.

The court ruled Monday that the Minnesota Pollution Control Agency hadn’t sufficiently justified granting the permit after opponents raised allegations that PolyMet was planning a much larger mine.

Environmental groups and a Native American tribe pointed to a report that PolyMet filed with Canadian regulators that suggested PolyMet was considering expanding the mine to four times the size that the air permit would allow. The appeals court sent the case back to the MPCA for further review.

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