As demand for coal has eased in the U-S, it's risen overseas - specifically, China. And plans are underway to ship coal to Asia from Wyoming and Montana, with construction recently approved for a new export terminal in Washington State. The Sierra Club and other groups are challenging that decision because of environmental concerns, with their attorney, Jan Hasselman of Earthjustice, arguing that the terminal should serve other purposes.

"We should be using that facility for light industrial use, manufacturing...to build things that we can send to China, rather than exporting our natural resources."

Hasselman says there are other implications to consider, too, such as whether it's right for Montana and Wyoming to be contributing to China's air pollution problems linked to the burning of coal.

"Americans have decided that they don't want to build new coal plants here at home."

Coal companies have pointed out that new markets for existing coal mining are critical to sustain coal jobs - which are considered good-paying positions.