Washington (CNN) -- Military convictions of two terror suspects will get a full federal appeals court review, testing whether the men could be charged with offenses that were not in place when Congress passed a 2006 anti-terror law.
In an unusual move, the U.S. Court of Appeals for the District of Columbia announced Tuesday all seven of its judges would hear an appeal from two Muslim prisoners held for years at the Guantanamo Bay military prison in Cuba.
Most appeals of that type are heard by three-judge panels, which separately tossed out the convictions of accused al-Qaeda propagandist Ali Hamza al-Bahlul, and former Osama bin Laden driver Salim Ahmed Hamdan.
The Obama administration then requested the full court to hear the case. Oral arguments will be held September 30.
The losing party will almost certainly ask the U.S. Supreme Court to offer the final word.
Both defendants were charged with providing material support to terrorism and conspiracy for al-Qaeda, around the time of the September 11, 2001, terror attacks, offenses that were not included as crimes before the Military Commissions Act went into effect several years later.
That law established the tribunal system used to try terror suspects held at Guantanamo, outside the civilian federal trial courts.
The ex post facto provision of the Constitution says the government may not retroactively criminalize conduct that was either legal or not on the record when committed.
The previous appeals panels concluded only pre-existing federal offenses and violations of the international law of war could be used to prosecute the men.
Al-Bahlul and Hamdan are so far the only Guantanamo inmates convicted at the military tribunals. Five other men had separately pleaded guilty to offenses.
Other cases, including alleged 9/11 mastermind Khalid Sheikh Mohammed, and other so-called "high-value detainees" are still awaiting trial.
Yemeni native al-Bahlul was convicted in November 2008 of conspiring with al-Qaeda, soliciting murder, and providing material support for terrorism. He was accused of making videos for the terror organization. His conviction was overturned in January, and he remains in Guantanamo custody.
Hamdan was also tried in 2008, the first man convicted under the new tribunal system. Later that year he was transferred to Yemen to serve out the remainder of his sentence. He had admitted to being the driver of the now-deceased leader of al-Qaeda, and was the subject of a 2010 documentary, "The Oath," chronicling his life and detention.
He is no stranger to the federal courts. In a blow to executive authority, the Supreme Court in 2006 ruled the existing military commission system to originally detain and charge Hamdan was not adequate, and the justices said Congress needed to come up new constitutionally permissible rules.
That decision prompted Congress to pass the Military Commissions Act and revise the tribunal system.
The law also sought to limit federal court jurisdiction to hear habeas corpus challenges to detention, but judges have consistently said they do have the power to be involved.
Ever since the 9/11 attacks, federal courts have been asked to determine if detainees had the right to contest their imprisonment and the rules set up to try them.
The current appeals court case is al-Bahlul v. U.S (11-1324).