The EPA has asked Minnesota's attorney general to explain how officials can issue and enforce pollution permits if it's restricted by state laws that exempt the mining industries.

A complaint filed by the Minnesota nonprofit group WaterLegacy asks the federal government to withdraw the state's power to regulate mining. WaterLegacy alleges the Minnesota Pollution Control Agency has failed to update permits for taconite operations, some of which expired decades ago.

State laws passed in 2015 and 2016 negate a water quality limit for sulfate, which is produced by runoff from taconite mines and other industries.