ST. PAUL, Minn. — A dispute over the future of the proposed PolyMet copper-nickel mine goes before the Minnesota Supreme Court on Tuesday.

The state Department of Natural Resources and PolyMet are challenging a ruling by the Minnesota Court of Appeals that canceled three major permits for the project.

The appeals court ruled in January that the state agency should have conducted a “contested case hearing," a trial-like proceeding on the project's environmental impacts, before it issued PolyMet a permit to mine and two dam safety permits. The court sent the case back to the DNR to conduct that proceeding, which could mean a lengthy delay. The appeals court also ruled that the DNR erred by not setting a fixed time period for the permit to mine.

Environmental groups fighting the project contend that the DNR failed to follow state law when it decided in 2018 that a contested case hearing on the permits was not necessary to resolve disputed issues.

But the DNR and PolyMet argue that the agency conducted an extensive environmental review and permitting process over 11 years, and that it met all the legal requirements, so there's no need for further proceedings. They say the Court of Appeals misconstrued the controlling statutes. And they're asking the Supreme Court to reinstate those permits.