The SNP's bid to amend a motion on the Queen's Speech, which would force a vote on withdrawing troops from Iraq, has attracted cross-party support.
The SNP wants to force a vote on withdrawing troops from Iraq
Former chancellor Ken Clarke, former government minister Claire Short and Labour's John McDonnell have all signed the amendment.
The support increases the chances of it being selected and voted upon in the climax to the Queen's Speech debate.
The amendment demands an exit strategy for British involvement in Iraq.
The SNP and Plaid Cymru MPs will say there is an 80-year-old precedent for the move.
The Liberal Party tabled an amendment to the King's Speech in 1923, demanding withdrawal from Mesopotamia, now called Iraq.
Westminster eventually demanded a withdrawal - and the SNP is hoping to achieve a similar feat this week.
However, they are relying on the speaker accepting their amendment, as happened 83 years ago.
Senior party figures argue that after last week's US mid-term elections, a vote would allow MPs to reflect on America's view that Iraq policy must change.
SNP leader Alex Salmond said: "We are now in the extraordinary position where the prime minister has agreed to give evidence via video link to the Baker Commission that is reassessing American policy in Iraq but has failed to spell out to the House of Commons any proposals for extracting British forces from Iraq.
"This amendment will require the government to detail exactly that. Those who are responsible for this blood-soaked quagmire now have the duty to tell us how they propose to remove our soldiers from this morass."
Two weeks ago, the Nationalists helped force a debate and vote on an inquiry into Iraq policy.
However, the SNP and Plaid Cymru motion for an immediate probe was opposed by a majority of 25, despite support from 12 rebel Labour MPs.
The Queen's Speech, to be given on Wednesday, sets out the key measures that the government hopes to implement in the coming session of parliament.