Coal companies announced major layoffs as a depressed market for coal and low natural gas prices drive down demand for the fossil fuel.

Coal giants Peabody and Arch Coal made the announcements Thursday beginning with their operations in the Powder River Basin of Wyoming.

"While our asset position and contracting strategies give us relative strength, we are taking these actions to match production with customer demand," Peabody President Kemal Williamson said."We regret the impact of these actions on our employees, their families, and the surrounding communities in the Campbell and Converse county areas."

Up until now western coal mines have been virtually immune to the big layoffs seen in the eastern part of the country in Appalachia. The announcements mark a significant turn of events for the industry.

Republicans have warned that increased environmental regulation by the Obama administration has placed increased pressure on the coal industry. The companies cited demand factors as the reason for the mining layoffs. At the same time, the nation's shale gas boom has driven the utility industry to switch to using more natural gas to produce electricity. The Energy Information Administration, the analysis arm of the Energy Department, recently reported that natural gas remained the leading producer of electricity in the country for the 12-month period that ended in January.

The combined layoffs from both companies would total nearly 500 jobs.

Peabody said it would cut nearly 235 hourly and salaried employees, or approximately 17 percent of the 1,400 workers at the firm's North Antelope Rochelle Mine, according to a statement.

Arch Coal said it would layoff a similar number of workers. It will cut 243 jobs from its 1,600 workers at the Black Thunder Mine.