The Minnesota Supreme Court will review a state Court of Appeals decision striking down PolyMet Mining’s air emissions permit.

Both PolyMet and the Minnesota Pollution Control Agency (MPCA) had petitioned the Supreme Court to evaluate the appellate court’s March ruling against an air permit for the company’s proposed mine near Babbitt and Hoyt Lakes.

The Supreme Court on Tuesday accepted the air permit petition, the second PolyMet permit decision it has agreed to review. In March, the court said it would review Polymet’s permit to mine and two dam-safety permits, which had also been rejected by the Court of Appeals.

The mine and dam permits were issued by the Minnesota Department of Natural Resources, which also asked the Supreme Court for a review.

The controversial $1 billion PolyMet project would be Minnesota’s first copper-nickel mine. It’s been derided by opponents who see it as an environmental fiasco in the making and praised by its supporters as significant boost for the Iron Range economy.

The open-pit mine and its operations for crushing and processing ore require an air permit because it would emit a range of pollutants into the air such as carbon monoxide, fine dust and mercury.

The Court of Appeals ruled that the MPCA, which granted the air permit in 2018, should have looked harder at whether PolyMet plans to expand the mine well beyond the limits imposed by the permit.

PolyMet’s Canadian securities filings indicate it may be planning a mine nearly four times larger than the operation covered by the air permit, which limits the mine to producing 32,000 tons of ore per day, the court noted.

PolyMet, formally based in Toronto but run from St. Paul, is majority-owned by global mining giant Glencore.