London: Labour is raising the alarm about a government attempt to extend to Northern Ireland a policy that imposes a two-child limit on universal credit recipients unless a woman can show she has been raped.

The move could place Theresa May on a collision course with the Democratic Unionist party, on whom she is relying on for her minority government to win votes in Westminster.

DUP MPs have previously set out their concerns about the two-child limit by signing up to an early day motion calling on the government to have the policy annulled. Owen Smith, the shadow Northern Ireland secretary, has used a parliamentary tool to demand a full debate and vote in the House of Commons, which — if granted — could be lost by May given the scale of opposition to the policy.

Labour is opposed to the policy altogether because it claims it will be destructive for low-paid families. But the party is particularly concerned about the impact of the rape clause in Northern Ireland where failure to report a crime is an offence punishable with a prison term. Labour says it is wrong to push ahead without a functioning executive in Belfast.

A letter from Smith and the shadow welfare secretary, Debbie Abraham, to the Northern Ireland secretary, James Brokenshire, warns: “This measure is being introduced in the absence of a functioning executive in Northern Ireland ... To impose such changes from Westminster, especially through the backdoor of a statutory instrument without scrutiny even by committee, is completely at odds with principles of the devolution settlement as agreed under the Good Friday agreement and subsequent agreements, including Fresh Start.” Under the Fresh Start agreement, welfare reform for Northern Ireland is decided in Westminster, but Smith pointed out that the power-sharing executive has the power to mitigate the impact of policies — and did so in the case of the bedroom tax.

He said it seemed likely that both the DUP and Sinn Fein would want to take action to ease any impact in this situation as well if the executive was up and running. But he also warned that the move could unintentionally criminalise women in Northern Ireland because of a unique law that makes it an offence, punishable by two years in jail, to fail to report a crime. “That would add gross insult to heinous injury for the womenconcerned and it cannot be allowed to pass into law,” he and Abrahams add in the letter.

They are calling for an urgent debate in the parliament. Although it is clear that the DUP has previously opposed this policy, the Guardian has not had a response as to whether the party would support Labour in this situation. The government pointed out that two-child limit was brought in across the UK in April, including in Northern Ireland, for those claiming tax credits. The statutory instrument, which has given Labour the opportunity to “pray” against it and demand a debate, relates to the policy’s application for universal credit recipients. That is needed because the new benefit has yet to roll out in Northern Ireland.

A government spokesman said the reform aimed to ensure “people on benefits have to make the same choices as those supporting themselves solely through work”. The government has said it would be delivered in a compassionate manner, with women who have conceived in a non-consensual manner able to speak to third-party professionals. “The third-party professionals involved do not need to seek any evidence to confirm the circumstances,” the spokesman added, saying they did recognise the particular issues in Northern Ireland.

Smith told the Guardian: “There is no way the Tories should be able to get away with introducing these controversial changes without parliament debating and voting on them, especially in the absence of devolved government in Northern Ireland.” He said that women who risk being criminalised needed their representatives to be able to speak for them in parliament. Campaigners in Northern Ireland said they were extremely worried about the issue. Jan Melia, the chief executive of the Women’s Aid Federation Northern Ireland, welcomed Labour’s attempt to stop the “rape clause”.

“Requiring women to prove that they conceived a child through rape to access child tax credits is cruel and inhumane. The policy will re-traumatise many victims of rape, while others will simply not come forward to claim what they are entitled to, leaving them and their children in poverty. The fact that this policy is being implemented at the same time that refuges and support services are having budgets decimated and doors closed is a cruel irony not lost on us,” she said.

Melia also questioned the overall two-child tax credit cap, “which is an attack on children, on families and on women” — and said it would be even more acute in Northern Ireland, where abortion has been inaccessible to women who cannot travel to other parts of the UK. Kevin Higgins, the head of policy at Advice NI, added that his organisation was also opposed to a policy that he said would heap pressure on low-paid families. “And the so-called rape clause will stigmatise children and potentially criminalise women,” he said.

— Guardian News & Media Ltd