(Reuters) - Minnesota’s highest court on Wednesday handed a victory to PolyMet Mining Corp, saying state regulators need not investigate allegations of “sham permitting” when considering an air emissions permit for the company’s proposed $1 billion copper-nickel-platinum mine. The Minnesota Supreme Court said the federal Clean Air Act did not require the Minnesota Pollution Control Agency to examine objections to the proposed NorthMet mine made by four environmental groups and the Fond du Lac Band of Lake Superior Chippewa tribe. Shares of Toronto-based PolyMet, which are listed in Canada and New York, closed up more than 16%. Wednesday’s 6-0 decision reversed a ruling by a state appeals court, which had said the agency should have taken a “hard look” at the allegations, including whether PolyMet might have intended to build a larger project. The Supreme Court said the federal Environmental Protection Agency could act later if the company went too far. It returned the case to the appeals court to address other issues. The proposed mine is located about 230 miles (370 km) north of Minneapolis, and nearer to the Canadian border. “PolyMet has engaged in a bait-and-switch scheme to avoid air pollution standards, and we are glad that the Supreme Court ruling allows us to make this case,” Kathryn Hoffman, chief executive of the Minnesota Center for Environmental Advocacy, one of the environmental groups, said in a statement. Lawyers for the tribe did not immediately respond to a request for comment. A spokesman for the Minnesota agency said it “scrutinized PolyMet’s emissions calculations and required the facility to have new requirements that protect Minnesota’s air. The result was a strong and enforceable air permit.” Jon Cherry, chief executive of PolyMet, called the decision “a major step forward in the defense of our air permit.” The case is In re: Issuance of Air Emissions Permit No. 13700345-101 for PolyMet Mining Inc, Minnesota Supreme Court, Nos. A19-0115, A19-0134.