Incoming committee chairman Ron Wyden and ranking Republican Lisa Murkowski said out-of-date regulations could be allowing miners to sell coal overseas at higher prices than reflected in their royalty payments.

In a letter addressed to Secretary of the Interior Ken Salazar, the lawmakers said alarming media reports suggested taxpayers could lose tens of millions of dollars in annual royalty revenue – particularly as US coal exports hit record levels.

“As companies seek to ship more coal overseas, taxpayers must be confident that the Bureau of Land Management and the Office of Natural Resources Revenue have stringent royalty collection and auditing controls in place as coal markets become increasingly oriented toward international buyers,” the senators wrote.

US coal exports this year are estimated to reach 124 million tons.

“Coal companies need to be paying taxpayers all of the money they are owed,” Wyden said.

“Federal agencies have a duty to ensure state and federal taxpayers get the full value for natural resources extracted from public lands. If regulators, or decades-old laws, are not doing enough to protect the public interest, our committee intends to find out, and to fix it.”

Between the 2001 and 2011 fiscal years, coal royalty revenue for the federal government and Indian tribes has more than doubled to $898 million, according to ONRR. It accounts for 21% of federal onshore royalty payments, 13% of tribal royalty payments and 8% of total federal royalty collections.

The domestic price of coal mined in the Powder River Basin is roughly $13 per ton, according to press reports, which is less than half of international prices that are $30 a ton or more. That price difference would translate to a royalty shortfall to the federal government of more than $2 per ton.

Although state officials agree there is no evidence that companies have failed to pay proper royalties, government auditing of sales over the past few years has begun.

Last month, Reuters reported that coal companies were avoiding $100 million in royalty payments by selling coal through “shell companies” before exporting it.

By valuing coal at a low domestic price then selling it at a higher rate to international customers, miners were alleged to have booked big profits through skirting royalty payment rules.