ST. PAUL (AP) — 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.