SPOKANE, Wash. -

Private contractors for the U.S. Department of Energy have spent at least $3.5 million in legal expenses to battle two critics of a massive construction project on the Hanford Nuclear Reservation.

The revelation came in a letter from the chairman of a U.S. Senate subcommittee that is investigating whether there was retaliation against two workers who raised safety concerns and then lost their jobs on the Hanford site. The letter was obtained by The Associated Press.

Democratic Sen. Claire McCaskill of Missouri writes that the Energy Department might be providing an incentive to contractors to engage in lengthy litigation with whistleblowers by reimbursing the contractors' legal expenses.

McCaskill is chair of the Senate Subcommittee on Financial and Contracting Oversight, which is investigating the treatment of former Hanford workers Walter Tamosaitis and Donna Busche.