MPs at Westminster are expected to vote later on Tuesday about whether or not to legalise same-sex marriage in NI.
It will come as part of a Commons debate aimed at keeping NI running in the absence of a devolved government, which collapsed in March 2017.
Its main purpose is to extend the government’s legal power to delay a fresh Stormont election until October at the earliest.
Backbench MPs have tabled amendments on other issues.
They argue these issues should not be stalled due to the lack of devolution.
Unlike England, Scotland, Wales and the Republic of Ireland, same-sex marriage is not legal in Northern Ireland.
Labour’s Conor McGinn, originally from South Armagh, put forward a proposal to the NI Executive Formation Bill that if Stormont is not restored by 21 October, then the government should legislate for same-sex marriage – with the caveat that a future assembly could overturn or amend the law.
His amendment has been chosen for debate by the Speaker’s Office.
The first half of Tuesday’s debate is expected to last for four hours, with Mr McGinn’s amendment expected to be debated and voted on at around 17:00 BST.
Another hour of debate on other amendments, including on one put forward by Labour’s Stella Creasy on abortion legislation in Northern Ireland, is scheduled for later, with voting on these expected at around 19:00.
The government has previously said it would allow Conservative MPs a free vote on the issue, with NI Secretary Karen Bradley saying she would personally vote in favour of it.
The Scottish National Party (SNP), which originally abstains on devolved matters in other nations, said on Tuesday morning that its MPs would be given a free vote on the issue.
The party’s Westminster leader Ian Blackford has also said he will vote for it.
Northern Ireland has been without a government for more than two and a half years, after a bitter row over a financial scandal split the DUP and Sinn Féin.
The Northern Ireland Secretary Karen Bradley has twice pushed back her obligation to call an election at Stormont, with it due to end on 25 August.
This new legislation would delay another poll until 21 October, with another possible extension to 13 January 2020.
It also provides greater clarity about decision-making to civil servants at Stormont, in the absence of functioning ministers.
Timeline of same-sex marriage:
- England and Wales legalised same-sex marriage in July 2013 and came into force in March 2014
- Scotland legislated for same-sex marriage in February 2014 which came into effect in December that year
- The Republic of Ireland legalised same-sex marriage in a referendum in May 2015 – becoming the only country in the world to do so by popular vote. Ireland’s first same-sex marriage took place in November 2015.