The sole remaining enemy combatant imprisoned on U.S. soil says the president "has no inherent authority to subject [him] to indefinite military detention," in legal papers filed with the Supreme Court Wednesday.

Ali Al-Marri's case against the government is expected later this year. But what remains unclear is what position the new administration will take in the case that is seen as major test of presidential authority and civil liberties.

Today's brief filed with the Court articulates why Al-Marri believes the Richmond, Va.-based Fourth Circuit Court of Appeals erred in its 5-4 ruling last year that the president could keep him locked up for years without trial.

"That ruling transgresses black-letter principles of statutory construction, flouts Congress's intent, and raises grave constitutional questions unnecessarily. It deviates dangerously from this nation's most cherished constitutional principles and traditions," wrote Al-Marri's lawyers. Quite simply, they claim, "it must be reversed."

Al-Marri was arrested in Peoria, Ill., a couple of months after the Sept. 11 attacks and is accused of being an Al Qaeda operative sent to the United States on Sept. 10, 2001 to take part in another attack.

In 2003, President Bush signed an executive order labeling Al-Marri an "enemy combatant" and removing him from civilian custody. The order made the Defense Department responsible for Al-Marri, who has been kept in isolation at the Navy brig in Charleston, S.C.

The Court granted the case knowing it would be argued by the new administration. What is not known is what position the Obama administration will take. The current schedule mandates a response by Feb. 20.

Last month, a spokesperson for then President-elect Obama told the Associate Press, "We are not going to comment on cases pending before our courts. President-elect Obama has repeatedly said that he believes that our current legal framework has failed to successfully and swiftly prosecute terrorists. He will make decisions about how to handle detainees as president when his national security and legal teams are in place."

Congressional approval for Obama's selection for solicitor general, Harvard Law School dean Elena Kagan, is still pending. Kagan's input would presumably play an important role in the final decision in how to handle the case, and she may be called upon to argue it in front of the Court. It is possible the administration will ask the Court more time to file its response.