Boris Johnson is set to face a major Commons rebellion next week over his policy to slash foreign aid.
Rebel Tory MPs believe they have enough support for new legislation that will see aid spending increase by 2022.
Conservative former chief Whip Andrew Mitchell is leading the parliamentary push, backed by a further 14 Tory backbenchers including former foreign secretary Jeremy Hunt and ex-aid minister Sir Desmond Swayne.
More could join following the backlash created by the policy in recent months, raising the prospect of a humbling Commons defeat for Mr Johnson.
The prime minister has been criticised by MPs on all sides for temporarily reducing foreign aid from 0.7% of national income to 0.5% – shelving his 2019 manifesto commitment to maintain spending at the higher rate.
The MPs have tabled an amendment that would force the government to reinstate its initial 0.7% spending target, which is legally binding.
Speaker Sir Lindsay Hoyle will then decide whether the amendment is selected for consideration when the Bill returns to the Commons for further consideration on Monday.
The government blames economic damage caused by the coronavirus pandemic for the aid cuts and expects just under £10bn to be allocated to departments for aid spending in 2021 and 2022.
But critics of the policy believe the government’s decision will result in tens of thousands of deaths in other parts of the world.
The government has also come under fire for not having a Commons vote on the decision.
Shadow Foreign Secretary Lisa Nandy said Conservatives should reverse the cut.
“On Monday, just days before world leaders arrive in Cornwall to discuss the global response to the pandemic, the government faces defeat over its short-sighted and self-defeating decision to slash aid,” she tweeted.
“The Conservatives should do the right thing and reverse this cut.”
Conservative former minister Caroline Nokes, one of the amendment signatories, said it has taken “quite a lot of manoeuvring to find an opportunity to actually have a vote on this”.
“I feel really strongly that we legislated for the 0.7% commitment and the cuts are affecting women and girls,” she told ITV’s Peston.
“I very much hope it will be binding. I don’t want to see the government try and find a way out of a commitment that we all signed up to just a few short years ago.”