The comments were made by Marine Corps Major Michael Mori, who represents Australian "enemy combatant" David Hicks being held at the US naval base at Guantanamo Bay, Cuba.
The US government insists that as "enemy combatants," the Guantanamo Bay detainees can be held and interrogated indefinitely without any legal representation.
Military tribunals existed in the US during World War II and were reinstated after the 11 September 2001 attacks to try terrorism suspects.
The tribunals hold their hearings behind closed doors and will have a lower threshold for conviction than regular courts, according to legal experts.
President George Bush has declared six Guantanamo detainees, including Hicks, eligible to be tried by these tribunals.
'Geared for conviction'
Mori, adressing a press conference in a Washington suburb with other military attorneys, said the military tribunals or commissions were "created and controlled by those with a vested interest only in convictions".
"Using the commission process just creates an unfair system that threatens to convict the innocent and provides the guilty a justifiable complaint as to their convictions"
Major Michael Mori,
US military lawyer
"Using the commission process just creates an unfair system that threatens to convict the innocent and provides the guilty a justifiable complaint as to their convictions," the lawyer said.
He said he believed the system was unfair because only the executive branch of government controlled them and was responsible for filing charges, setting the rules and appointing judge and jury.
He warned that military trials could "lower the standard" used to treat US citizens in foreign countries and might set "a dangerous precedent".
"The reality is, we wouldn't tolerate these rules if they were applied to US citizens," he said.
Mori said the US should use well-established courts-martial, if there was reliable evidence to convict a detainee.
Bush has cleared six Guantanamo
detainees for trial by the tribunal
In a separate interview with a Sydney radio station, the attorney said he believed that since Hicks had not injured any US citizens, he should be tried in Australia.
Hicks was captured by US troops in late 2001 in Afghanistan where he was fighting alongside Taliban troops.
The US and Australia agreed last November Washington would not seek the death penalty for Hicks or monitor his conversations with his attorneys.
If he is convicted, he is likely to be allowed to serve his prison term in Australia under this accord.
Meanwhile, the US National Council of Churches said the Pentagon had refused its request to visit the Guantanamo Bay detainees.
The council last month had sought permission to send a delegation to the camp, home to about 660 foreign terror suspects, out of "humanitarian concern for the detainees physical and mental well being", said the group's general secretary, Bob Edgar.
But Defence Department official Jeffrey Starr said access to detainees "is only provided to the International Committee of the Red Cross, and on a case-by-case basis to government officials for legitimate government purposes," according to excerpts from his letter made public by the council.