The U.S. Supreme Court was hearing a case Wednesday that many consider to be the most important the court will hear this session — whether the military courts set up for terror suspects at Guantanamo Bay, Cuba, are constitutional.

If it sounds familiar, it is. This is the third time the Supreme Court will consider the rights of the detainees, but expectations are high that the court’s opinion in this case will offer a definitive ruling on what legal protections those prisoners are afforded. It is also viewed as a fundamental legal test of the Bush administration's prosecution of the War on Terror.

The case revolves around Lakhdar Boumediene, one of the remaining 305 War on Terror prisoners at Guantanamo Bay. He's been there since 2002 and lawyers on his behalf say he and the others at the highly controversial prison camp are being unconstitutionally denied access to the U.S. court system.

The case is built on previous rulings by the court, including a 2004 decision in Rasul v. Bush that stated the prisoners at Gitmo are entitled to have access to the U.S. court system, leading the U.S. government to establish a military tribunal process.

As it stands, the prisoners can appeal adverse rulings to the D.C. Circuit Court of Appeals. Solicitor General Paul Clement argues that the existing process provides Boumediene "along with the other enemy combatants being held at Guantanamo Bay, [the opportunity to] enjoy more procedural protections than any other captured enemy combatants in the history of warfare."

That is "an absolute lie," one of the lawyers for the detainees told reporters Monday. The plaintiffs contend that the current law fails to protect the constitutional rights the Court said their clients were entitled to receive in Rasul.

Hundreds of spectators lined up at the Supreme Court ahead of the hearing. About 50 court watchers camped out overnight to be able to get seats in the courtroom and hear Seth Waxman, who is defending the detainees.

"We're rooting for our law professor; we hope he wins," said Alex Fumelli, a senior at Georgetown University, where Waxman teaches.

Still unclear from the Rasul decision and what's at issue before the court is whether the detainees are entitled to the basic legal protection known as habeas corpus. This constitutionally protected right forces the government to justify in an open courtroom legitimate reasons why an individual needs to be behind bars. Also known as the "Great Writ," it is a universal right that was famously suspended by Abraham Lincoln during the Civil War.

Lawyers for the detainees argue the government, through the 2006 Military Commissions Act, unconstitutionally suspended the Great Writ for their clients. What they seek is "a single remedy: a fair and impartial hearing before a neutral decision maker to determine whether there is a reasonable basis in the law and fact for detaining them. They have never received such a hearing, although this court ruled more than three years ago that they are entitled to one."

The government contends the Rasul decision doesn’t cover habeas rights and that earlier court rulings make clear that foreign prisoners held outside the United States have no such right.

"As aliens held outside the sovereign territory of the United States, [the detainees] may not invoke the protections of our Constitution … and there is no basis to upset that longstanding constitutional rule here."

It further argues that the military tribunals passed by Congress are an adequate substitute for what habeas seeks to protect.

"Although Congress expressly chose to foreclose detainees from challenging their status via habeas, it decided that aliens detained at Guantanamo Bay as enemy combatants should receive administrative hearings before a military tribunal, subject to judicial review in the District of Columbia Circuit. That system builds additional protections upon those that are available even to conventional prisoners of war under the Geneva Convention, and it was designed to track the requirements for due process deemed sufficient for American citizens."

Boumediene is an Algerian native who was living in Bosnia at the time of his arrest in October 2001. He and five others are accused of plotting to blow up the American embassy in Sarajevo. They were relocated to Guantanamo Bay in January 2002 where Boumediene remains incarcerated.

He denies any involvement in plots against the United States. His case and those of other detainees have been consolidated into one hour of arguments in front of the court. Former Solicitor General Seth Waxman will argue on behalf of the detainees and Clement will argue for the government.

This case has already provided one surprising twist. In April, the court decided not to consider the matter but reversed itself in June. It is believed to be the first time in 60 years that the court changed course in such a manner.

The reversal required at least five of the nine justices to grant review. Normally, only four need to agree to hear a case, and even then very few are granted arguments. The extraordinary reversal has led to speculation that it will be difficult for the government to win the case. It is widely believed that Justice John Paul Stevens, who wrote the court’s opinion in Rasul, convinced Justice Anthony Kennedy to change his mind. Kennedy has proven to be the swing vote in an often divided court. He was in the majority in all of the previous term’s five-four decisions.

The Associated Press contributed to this report.