A senior Tory MP has threatened to vote against the Government over Universal Credit unless ministers recognise they need to address a "fundamental flaw".
Sarah Wollaston, chairwoman of the Health Committee, criticised her party for ordering its MPs to abstain on any vote on a Labour-led motion about the flagship welfare reforms.
She said she wants assurances that the Government will recognise and address the time it takes for new claimants to receive their first payment under UC.
MPs have heard the six-week wait for first payments has been causing issues for new claimants.
Any vote on Labour's motion calling for the Government to pause UC roll-out would be symbolic and non-binding on ministers.
Dr Wollaston said Government moves to scrap helpline charges and improve access to advance payments were welcome.
She added: "But it doesn't get us away from the fundamental problem of a minimum six-week wait.
"And that means our constituents, who are living on the edge, and we're talking about real people's lives here, are going to start this process in debt and in arrears as we've heard.
"It's possible to apply test, learn and rectify to this process and I want to hear from the frontbench in summing up that they recognise and are going to address the six-week wait, because the advance doesn't solve the issue, it doesn't cover the entire amount."
Dr Wollaston said MPs have a "cushion" but many people she saw when a GP or who she represents now "have no cushion whatsoever", adding: "We can't ignore the very real, compelling case histories we've heard.
"We can't allow that to continue."
On the vote, Dr Wollaston said: "I know this side of the House is going to be abstaining tonight.
"Personally I don't agree with this.
"I think the House should have an opportunity to express its view and there have been occasions on which these debates have managed to lead to changes in policy even though they're advisory.
"If there is no way for me to express my view on behalf of my constituents, that I think this fundamental flaw must be addressed before it is rolled out to the Totnes constituency next year, I'm afraid I will have to vote against the Government.
"I don't wish to do that because I support the fundamental, the underlying policy of Universal Credit, we've heard many of its benefits.
"But we are undermining it, I say again, by not addressing the fundamental flaw at its heart and I hope the minister will give an assurance at the despatch box so I don't have to vote against the Government."
DUP MP Sammy Wilson said his party will abstain on any Commons vote to pause UC, saying his party saw problems with the benefit but "will not be used for headline-grabbing defeats of Government flagship policies".
The Tories only command a majority in the Commons because of a confidence and supply arrangement with the DUP.
It comes as former Tory leader Iain Duncan Smith advised his colleagues to resist the temptation to rebel over UC and instead continue suggesting changes to David Gauke, his successor as Work and Pensions Secretary.