The Senate has revived a divisive debate over civil liberties and the president's powers as commander in chief, voting that American citizens suspected of terrorism and seized on U.S. soil may not be held indefinitely.
The vote late Thursday was on an amendment to a sweeping defense bill, and it was backed by a coalition of liberal Democrats and libertarian Republicans.
Under the amendment, the government would be prohibited from detaining a U.S. citizen or legal resident indefinitely without charge or trial even with the authorization to use military force or a declaration of war.
The vote sets up a fight with the House, which rejected efforts to bar indefinite detention in its own bill.
The Senate is expected to vote Friday on a new package of sanctions on Iran.