Peabody Energy, the biggest producer of coal in the U.S., announced Wednesday that it may have to seek bankruptcy protection.

The company “had a total debt of $6.3 billion at the end of 2015,” Reuters reports, and its “shares have crashed from their record high of more than $1,300 in 2008 to $4.01 as of Tuesday’s close, reflecting the downturn in the coal market over the past few years.”

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“If we are not able to timely, successfully or efficiently implement the strategies that we are pursuing to improve our operating performance and financial position, obtain alternative sources of capital or otherwise meet our liquidity needs, we may need to voluntarily seek protection under Chapter 11 of the U.S. Bankruptcy Code,” the company said in a regulatory filing with the Securities and Exchange Commission.

The company also stated that it “skipped a $71.1 million interest payment on its senior notes, kicking off a 30-day grace period,” Fortune magazine reports.

The filing also follows a warning by federal regulators last month that Peabody, which is also a member of the American Legislative Exchange Council, may be in violation of mining law. That’s because the company continues “to extract coal while failing to meet the criteria for self-bonding,” referring to a company’s ability to secure its own assets for future mine clean-up rather than posting collateral for those expenses, as the Casper Star Tribune reported. 

Peabody “is crashing,” according to Jenny Marienau, U.S. divestment campaign manager with 350.org, “because the company was unwilling to change with the times—they doubled down on the dirtiest of all fossil fuels, and investors backed their bet, as the world shifted toward renewable energy.”

“Peabody Energy’s steep decline toward bankruptcy is a harbinger of the end of the fossil fuel era,” she said, adding, “They have consistently put profit over people, and now their profits have plummeted. Our world has no place for companies like Peabody.”