Attorneys for Lt. Col. Jeffrey R. Chessani want to question Rep. John Murtha over his public statement that the Marines killed "in cold blood" during the attack in Haditha. Murtha said he had been briefed by the highest levels of the military about the case and that officers covered it up.
Chessani's attorneys, who released the ruling Wednesday, said they will appeal if the judge doesn't reconsider.
Chessani is the highest-ranking U.S. serviceman to face a combat-related court-martial since the Vietnam War.
"When the congressman said he was briefed by the highest levels, we need to know who they are," said Brian Rooney, Chessani's civilian defense attorney.
Rooney said Murtha's deposition would "confirm what he said to the press is accurate."
Murtha's spokesman, Matthew Mazonkey, said the congressman had no comment. A telephone call to a Marine Corps spokesman was not immediately returned.
Chessani has been charged with dereliction of duty and violation of a lawful order on allegations that he mishandled the aftermath of the Nov. 19, 2005, shooting deaths in Haditha.
He faces court-martial on April 28. If convicted on all counts, he faces up to three years in prison.
Four enlisted Marines were initially charged with murder in the case and four officers were charged with failing to investigate the deaths. Charges against several of the men have been dropped, and none will face murder charges.