The layoffs come amid forecasts that the share of U.S. electricity coming from coal will fall below 40 percent for the year — the lowest level since the government began collecting data in 1949. Four years ago, it was 50 percent. By the end of this decade, it is likely to be near 30 percent.

"Current market pressures and a challenging regulatory environment have pushed coal consumption in the United States to a 20-year low," Arch President and CEO John W. Eaves said in a news release announcing the layoffs.

Eaves said the company regrets the impact on its employees and their families and communities, but said the decision was necessary "to weather the current downturn and to position the company for long-term success."