The measure, part of the Defense Appropriations Act that President Bush signed last week, was intended to allow detainees at the U.S. naval base in Cuba to appeal their detention status and punishments to a federal appeals court in Washington.
That avenue replaces the one tool the Supreme Court gave detainees in 2004 to fight the legality of their detentions: the right to file habeas corpus lawsuits, which demand the government justify someone's continued imprisonment, in any federal court.
The new provision won broad support only after its chief Democratic sponsor, Sen. Carl Levin of Michigan, said it had been altered so it would not apply to pending cases.
But on Tuesday, the Justice Department notified judges at U.S. District Court in Washington that it will ask them to dismiss 187 cases involving more than 300 people because the law eliminates the jurisdiction of district courts to consider the legality of detentions at the naval base.
The decision to try to stop pending cases in their tracks drew an immediate rebuke from advocates for the detainees, who said the provision should apply only to new challenges. "The battle about what that provision means has only just begun," said Elisa Massimino, director of the Washington office of Human Rights First.
Many of the 500 or so prisoners held at Guantanamo were captured in Afghanistan and have been detained for several years without being charged.
Since the Supreme Court ruling, prisoner lawsuits against the government have piled up.
Administration officials and supportive lawmakers have argued that the United States gives the detainees unprecedented access to U.S. courts, in some cases more than U.S. military personnel who have been convicted of crimes by military courts.
Under the new law, detainees still may appeal their classification as enemy combatants or their conviction by a military commission to the U.S. Court of Appeals for the District of Columbia.