By Jonathan Beale
BBC News, Washington
A bipartisan group of US congressmen have put forward legislation to prevent the president attacking Iran without the authorisation of Congress.
Democrats say Mr Bush is not engaging with Iran
The move comes amid concern at George W Bush's attitude towards Iran.
He has recently decided to ratchet up the pressure on Tehran over what he calls unhelpful behaviour in Iraq.
A second navy task force has recently been sent to the Gulf and last week US forces arrested Iranian officials in northern Iraq.
Democrats have already expressed concern about Mr Bush's decision to confront Iran rather than to engage it diplomatically.
Recent events have only heightened fears about his intentions.
The bipartisan group of 11 congressmen, led by a Republican, have put forward legislation that states that no previous resolution passed by Congress authorises a US attack on Iran.
One of the Democrats who supports the legislation said that a new resolution was needed because the Bush administration had lied so many times in the run up to the Iraq war.
But it may prove more of a symbolic move as, to become law, it would need the support of the Senate and the House of Representatives and to be signed by the president himself.
US officials have been playing down talk of attacking Iran.
The US Defence Secretary, Robert Gates, who has been meeting Arab leaders, said that no-one wanted another military conflict in the region.
But Mr Gates defended the US military build-up as a way of containing Iran's ambitions.