Tougher emission rules at U.S. power stations will likely force coal companies to make up for lost domestic customers by exporting more to countries in Asia where environmental regulations are less stringent, analysts said.

Railroads, which haul about 70 percent of U.S. coal, could also try to mitigate the damage from lower shipments to utilities by carrying more coal for exports.

Proposed rules that will limit new power plants’ CO2 emissions, the first move by the world’s largest economy to regulate the gas blamed for contributing to global warming, were announced Tuesday by the Environmental Protection Agency (EPA).. Currently, coal-fired plants produce about 44 percent of U.S. electricity.