Still, the OSMRE finding would add pressure on all sides to do something about the mines' bonding should the agreement not take effect later this month as expected.

Mead criticized the finding as counterproductive and promised to appeal.

"This action by the Office of Surface Mining Reclamation and Enforcement is unwarranted and does nothing to ensure reclamation proceeds as planned and at Alpha's expense as Wyoming's agreement provides," Mead said in a statement. "If Wyoming followed the lead of OSMRE, it would result in shutting down coal mines and putting coal miners out of work, thus shifting the reclamation liability to taxpayers."

The problem arose because Wyoming allowed Alpha Natural Resources to avoid covering its potential cleanup costs by setting aside cash or bonds for its Belle Ayr and Eagle Butte mines. Instead, the company made good on its cleanup obligations solely on the basis of its financial strength, a practice called self-bonding.

Alpha Natural Resources, Arch Coal and Peabody Energy, all of which are undergoing Chapter 11 reorganization, together have $2.3 billion in self-bonding obligations in Wyoming, West Virginia, Illinois, New Mexico and Indiana.