The U.S. government is proposing new rules for how it values coal mined from public lands in the West to make sure companies aren't shortchanging taxpayers on sales to Asia.

Friday's Interior Department announcement comes after coal exports surged in recent years as the industry sought alternatives to a weak U.S. market.

Under rules in place since the 1980s, companies can sell the fuel to affiliates and pay royalties on that price, then turn around and sell the coal for more overseas.

Gregory Gould, Director of Interior's Office of Natural Resources Revenue, said the proposed changes would allow the government to capture the full value of overseas sales.

National Mining Association Vice President Nancy Gravatt said the existing system has generated billions of dollars in tax revenue.