Pittsburgh-based Consol attributed the moves on Tuesday to a decline in global steel demand. Both mines produced metallurgical coal, which is used to make steel.
The idling of the Buchanan Mine in southwestern Virginia is effective Tuesday.
Consol says it's still reviewing whether to fully idle the Amonate Mining Complex in southern West Virginia.
Operations are expected to remain idle for 30 to 60 days. Most of the Buchanan Mine's 620 workers will be furloughed. The Amonate mine employs contract workers.