The coal industry has faced a myriad of problems in recent years, including proposed regulation from the Obama administration to cut greenhouse gas emissions from the nation's coal-burning power plants. The industry refers to those regulations as Obama's "war on coal."
While the new regulations have been put on hold by the Supreme Court, the industry has faced a number of other economic woes, including significantly lower prices for natural gas, which is a competing fuel used by electric utilities, and slowing economic growth in China, a major market for U.S. coal.
Renewable sources of energy are also getting much cheaper, further squeezing demand.
Arch Coal (ACI), which owns the second-largest U.S. coal reserves behind Peabody, filed for bankruptcy in January.
Top U.S. coal company Peabody Energy files for bankruptcy