The mineral mining sector in the United States is showing signs of serious decline brought on by bankruptcies in the coal sector, Fitch Ratings said.

"A spate of coal defaults has resulted from unsustainably high debt leverage from past acquisitions amid an environment of weak coal pricing," Fitch said in an industry profile. "The low pricing and defaults were driven by over-supply of steam coal and metallurgical coal, burdensome regulations, and competition from low priced natural gas for electric generation business."

A federal Clean Power Plan set a goal of cutting emissions of carbon dioxide, a potent greenhouse gas, by 32 percent of their 2005 baseline by 2030, 9 percent more than in the original proposal. States need to meet specific emission reductions based on state-by-state energy consumption criteria.

When the EPA outlined the Clean Power Plan last month, Michigan Attorney General Bill Schuette said he was "deeply concerned" by what he saw as a federal decision that put state jobs at risk and possibly lead to higher consumer bills. Michigan has challenged some federal power decisions at the U.S. Supreme Court.

Michigan depends on coal for much of its energy needs. The governor's office said it would look for new power sources at it phases coal out of the energy mix.

New York City Mayor Bill de Blasio called on all five New York City pension boards will consider a proposal to divest from coal. Notre Dame University last month said it will stop relying on coal for electricity within five years and cut its carbon footprint by more than half before the end of the next decade

Fitch said there's been a "wave of bankruptcies" in the United States, with at least three major producers announcing major defaults this year.