The proposed prisoner transfer was first reported in December by Reuters.
The Taliban detainees are seen as among the most dangerous remaining at Guantanamo, and the transfer idea drew strong opposition on Capitol Hill even before it was formally proposed.
Many lawmakers fretted that transferred detainees would reappear on the battlefield, and objected to the possible release of prisoners blamed for bloody crimes in Afghanistan.
U.S. officials stress that the transfer, if it occurs, will be done in accordance with U.S. law, which requires Congress to be notified before any detainees are moved from Guantanamo.