CHARLESTON, W.Va. — The federal Mine Safety and Health Administration has told 16 U.S. mining companies that they repeatedly violated health and safety rules and warned them to clean up their acts.

MSHA says 14 companies operate coal mines or processing plants, the vast majority of them in West Virginia and Kentucky. The list also includes a Kentucky limestone quarry and a Michigan iron ore mine.

This is the third time in a year that MSHA has threatened repeat violators and the agency maintains the policy is working.

The agency says seven of eight operations notified last June cut their rate of significant and substantial violations by an average 50 percent. One operation closed.

MSHA says 20 more operators targeted in December cut their violation rates an average 65 percent.