The American Bar Association also opposes the provision in the defense bill.
"If passed, this legislation will have a severe chilling effect on the ability of lawyers to provide zealous advocacy and effective assistance of counsel to their clients at Guantanamo," said Carol Lamm, president of the ABA.
Still, Rep. Miller believes expanded authority for the DOD to investigate lawyers working at Guantanamo holds them to "the same standard of any other individual."
"Attorney-client privilege doesn't give them the ability to break the law and compromise national security," he said.
After the full House votes on the legislation, it heads to the Senate Armed Services where the debate is expected to continue.