ST. PAUL — U.S. Steel has gone to court in a dispute with the Minnesota Pollution Control Agency over pollution limits for its Minntac iron mining operations.

Minntac has been operating under a water quality permit that technically expired in 1992. Pittsburgh-based U.S. Steel said in a statement Tuesday that if several of its long-standing requests for changes remain unresolved, the company could be forced to make significant, unnecessary investments that could put Minntac at a competitive disadvantage.