Investigators raided the offices May 2 in search of a cellphone tied to a case being tried at the base, north of San Diego, Lt. Col. Clay Plummer told The Associated Press.
"This is just unacceptable," said Plummer, the Marine Corps' regional defense counsel for the West. "Just think of the U.S. federal Marshals or FBI raiding a public defender's office, that's what this is the equivalent to. It's crazy."
Marine Corps officials called it a "rare event" and said a neutral, independent judge advocate will be appointed to review the seized evidence to identify whether any potential privileged material was improperly disclosed.
Officials said they could not comment further because of pending litigation and the independent review.
Defense lawyers were contacting hundreds of clients to inform them that military law enforcement officials had opened case files, Plummer said.
The search's authorization was granted by the area commander, Plummer said, but investigators did not limit their check to the attorney's office for the case with the cellphone. They searched every attorney's office, he said.
Plummer said his lawyers will be filing motions with the courts against the action.
"Our intent is we are going to fight this behavior through litigation in our courts with the hope our courts can do something so this never happens again," Plummer said.
Lawyers in the offices are handling cases for offenses ranging from an unauthorized absence to murder. One of the most prominent cases handled by defense lawyers at Camp Pendleton is that of Lawrence Hutchins III, a Marine sergeant who is being retried in an Iraq war crimes case on charges that include murder and obstruction of justice.