The US House of Representatives has supported a call to ban cruel, inhuman or degrading treatment of foreign terrorism suspects.
Human rights groups are accusing the US of mistreating inmates
It voted 308 to 122 to back a measure passed by the Senate to include the ban in new defence spending legislation.
The symbolic move by both chambers is not binding on the White House, but is seen as highly embarrassing.
The Bush administration had threatened to veto any legislation limiting interrogation tactics.
Republican Senator John McCain, who is a former prisoner of war in Vietnam, has been lobbying for the bill.
A member of the House of Representatives, John Murtha, said torture would not help the US win the hearts and minds of people it was used against, and Congress was obliged to speak out.
The backing in both wings of Congress - which are controlled by the Republicans - comes amid continuing negotiations between Sen McCain and the Bush administration for strict guidelines on the treatment of detainees.
However, the motion does not require the negotiators to include the ban in the final military spending bill.
A US human rights group has praised the latest move.
"The House and Senate have now spoken loud and clear, with a single message - the United States will not permit cruel, inhuman and degrading treatment," Elisa Massimino, the Washington director of Human Rights First, was quoted as saying by the Associated Press news agency.