Peabody Energy, the largest U.S. coal producer, said it may have to seek Chapter 11 bankruptcy protection after it delayed an interest payment due on Tuesday.
Falling demand for coal, tough environmental controls and growing competition from natural gas have pushed several big coal miners, including Arch Coal, into bankruptcy protection over the past year.
Peabody, which flagged bankruptcy risk under the "risk factors" section of a regulatory filing on Wednesday, said it skipped a $71.1 million interest payment on its senior notes, kicking off a 30-day grace period.
The company raised "substantial doubt" about its ability to remain a going concern.
Peabody's lenders are pushing the company to restructure its debt through bankruptcy but the company has also been pursuing bond exchanges.
As of Dec. 31, the company had a total debt of $6.3 billion and cash and cash equivalents of $261.3 million.