The U.S. Supreme Court may soon decide whether military tribunals can try detainees at Guantanamo Bay for violations of U.S. domestic law, and for the first time clearly define the scope of a military commission’s power to administer justice.

Ali Hamza Ahmad Suliman al Bahlul, a Yemeni national held as an enemy combatant since 2002, brought the case after his 2008 conviction for conspiracy and providing material support for terrorism, among other crimes. Bahlul was tried before a military tribunal and convicted by a jury of nine officers.

On appeal to the U.S. Court of Appeals for the D.C. Circuit, Bahlul argued that military commissions are only empowered to adjudicate international war crimes. Since conspiracy and providing material support for terrorism are crimes only under U.S. law, and are not recognized as international war crimes, he argued that his convictions should be overturned.

What’s more, the Constitution explicitly reserves “the trial of all crimes” to the judicial branch. Therefore, Bahlul said, he should be tried on American soil before an American court. A fractured D.C. Circuit ultimately upheld his conspiracy conviction, prompting an appeal to the Supreme Court.

A military tribunal’s authority to try enemy combatants for crimes like conspiracy stems from the 2006 Military Commissions Act. The Act makes 31 crimes, conspiracy among them, triable before a military tribunal. Bahlul says this legislation creates two problems.

In the first place, he argues that the law effectively establishes a separate system of justice, with entirely different rules and procedures, for non-citizens indicted of certain crimes, in violation of the Constitution’s guarantee of equal protection.

Chain link fencing and concertina wire surrounds a deserted guard tower within Guantanamo's Camp Delta. Thomson Reuters

Secondly, he says that the law’s retroactive application violates the Constitution’s prohibition of ex post facto laws, or a law that “criminally punishes conduct that was lawful when it was done.” In other words, Bahlul argues that he cannot be convicted under a law that was passed five years after his arrest.

Government lawyers counter that Bahlul’s claims cannot now be reviewed because he failed to raise them before the military tribunal during his trial, instead choosing to “forgo any legal challenges in service of a self-styled boycott.”

They further say that the D.C. Circuit’s decision does not conflict with existing Supreme Court precedent, or with the case law of other appeals courts. The justices are unlikely to take a case which does not involve conflict between the federal appeals courts or an obvious break with past Supreme Court decisions.

As University of Texas Law Professor Steve Vladeck explained this week, non-citizens are routinely charged in terror-related cases with crimes like conspiracy, raising important questions about the scope of a military court’s jurisdiction.

“[A]s transnational terrorism continues to blur longstanding distinctions between the military and civilian spheres, preserving a constitutional stopping point is crucial,” he wrote in a Wednesday New York Times op-ed.

Vladeck also notes that the case could have important policy implications, since the Trump administration is reportedly considering revitalizing the detainee program, of which military tribunals are an important component.

The justices considered the petition during a conference Thursday. A decision as to whether they will hear the case could come as early as Tuesday.