In a letter sent to Defense Secretary Robert Gates today, the American Civil Liberties Union (ACLU) said the Department of Defense's treatment of 23-year-old Pfc. Bradley Manning was a clear violation of the U.S. Constitution.

Manning faces numerous charges for stealing classified files and is suspected as the source of a massive trove of State Department documents published on the WikiLeaks website in recent months. He has been held at the Quantico brig since July under a maximum security regimen, which leaves him in his cell for 23 hours a day, because authorities say his escape would pose a risk to national security.

"The Supreme Court has long held that the government violates the Eighth Amendment’s ban on cruel and unusual punishment whenever it unnecessarily and wantonly inflicts pain," the letter to Gates stated. "No legitimate purpose is served by keeping Private Manning stripped naked; in prolonged isolated confinement and utter idleness; subjected to sleep deprivation through repeated physical inspections throughout the night; deprived of any meaningful opportunity to exercise, even in his cell; and stripped of his reading glasses so that he cannot read."

"Nor has the Department of Defense any legitimate purpose in requiring Private Manning to stand naked in his observation cell at 'parade rest,' with legs spread and genitals displayed, in full view of guards and other officers," the letter continued. "The very purpose of such treatment is to degrade, humiliate, and traumatize -- a purpose that cannot be squared with what the Supreme Court has described as 'the basic concept underlying the Eighth Amendment, which is nothing less than the dignity of man.'"

Defense Department officials claim that Manning has been held in solitary confinement and stripped of his clothes to prevent him from committing suicide.

"The problem with the argument that Manning is being kept in long-term solitary confinement to prevent his suicide is that long-term solitary confinement causes suicide," Terry A. Kupers, institute professor at The Wright Institute, explained in an article at CNN. "Suicide is merely the tip of the iceberg. Solitary confinement breaks prisoners down and practically guarantees they will never function normally in society again."

"Absent any evident justification, such treatment is clearly forbidden by our Constitution," the ACLU said. "Given that those standards apparently permit Private Manning to be subjected to plainly unconstitutional conditions, it is clear that the Department of Defense must adapt its standards to meet the demands of the Constitution."

The State Department's top spokesman, P.J. Crowley, was forced to resign over the weekend after he called Manning's treatment "ridiculous and counterproductive and stupid."

Despite being a member of the House Committee on Oversight and Government Reform, Congressman Dennis Kucinich (D-OH) has been unable to visit with Manning to investigate reports that he had been subjected to abusive treatment.

The Pentagon has rejected allegations of harsh conditions and said Manning received treatment similar to others under the high-security regime.

"He's not being treated differently than any other maximum security detainee and not differently really that much from the medium security detainees," Pentagon press secretary Geoff Morrell told MSNBC after he paid a visit to the site himself.