The top military commander in Afghanistan urged members of Congress on Wednesday not to support a resolution calling on President Barack Obama to bring US troops home by the end of the year.
General David Petraeus said that "al-Qaida would trumpet a victory" if the Bill passed.
It was introduced last Wednesday by Republican and Democratic legislators including Dennis Kucinich, Ron Paul and Barbara Lee.
It invokes the War Powers Resolution of 1973 which, if enacted, would require Mr Obama to withdraw troops from Afghanistan by December 31 2011.
The law has bipartisan support and a recent Rasmussen poll showed that most US citizens want their troops home by the end of the year.
It is designed to appeal to the Republicans' "fiscal conservatism" agenda.
Mr Kucinich observed that, while Congress "pulls unemployment benefits from suffering Ohio families and proposes slashing health care benefits, vital children's programmes and veterans' services all because we're 'broke,' it continues to fund a war that has cost us more than $455 billion (£282bn).
"The Centre for Arms Control and Non-Proliferation estimates that the wars in Iraq and Afghanistan cost the average US family of four almost $13,000 (£8,050) last year."
Gen Petraeus told the House Armed Services Committee that "the Taliban and al-Qaida would obviously trumpet this as a victory, as a success.
"Needless to say, it would completely undermine everything that our troopers have fought so much for and sacrificed so much for."