Managers of Montana's Decker Coal Mine say up to 75 employees will be laid off from the mine near the Wyoming border in mid-January.
A spokesman for mine operator Ambre Energy North America on Friday attributed the layoffs to "ongoing expense management activities," but offered no details.
There are about 160 workers at the mine in the Powder River Basin, which has the country's most productive coal fields.
It's co-owned by KCP, Inc. and Western Minerals, LLC, a subsidiary of Cloud Peak Energy.
Ambre spokesman Brian Gard says the layoffs are unrelated to a legal dispute between the owners over whether to expand production.
Federal mining records show coal production at Decker has dropped sharply, from 7 million tons in 2006 to 3 million tons last year.