Assembly members in Northern Ireland are to vote on a proposal to legalise same-sex marriage in the region.
The vote will be the fifth occasion a bid to change Northern Ireland’s marriage laws has come before the devolved legislature at Stormont, Belfast.
MLAs have rejected the introduction of gay marriage on the four previous occasions.
Following the signing into law of same-sex marriage legislation in the Republic of Ireland last week, Northern Ireland is now the only part of the UK or Ireland where civil marriage is denied to same-sex couples.
Previous votes at Stormont have proved controversial, as unionists opposed to legalisation have used a contentious Assembly mechanism to effectively veto it.
A petition of concern has again been deployed by the Democratic Unionists ahead of today’s vote - meaning the proposal is set to be rejected even if a majority of MLAs back it.
The mechanism means a proposal can only pass if a majority of unionists and a majority of nationalists vote yes.
The issue of gay marriage divides public opinion in Northern Ireland, with vocal campaigners on both sides of the argument.
While advocates claim same-sex couples are being denied the rights afforded to heterosexuals, a number of Christian organisations insist the institution of marriage should not be redefined.
Two same-sex couples have pledged to invite MLAs to their weddings if they vote to legalise them.
Couples Jayne Robinson and Laura McKee and Michael McCartan and Malachai O’Hara plan to attend the debate at Parliament Buildings dressed in wedding regalia.
Two other same-sex couples are currently seeking to overturn the Assembly’s ban in Belfast High Court by way of a judicial review.
In the summer about 20,000 people marched in Belfast city centre demanding a law change.
In 2005 Northern Ireland became the first part of the UK to allow same-sex civil partnerships.
The four previous votes on gay marriage at Stormont would have fallen on a simple majority basis, regardless of whether a petition of concern was tabled.
Peter Lynas, from the Evangelical Alliance, said examining potential reform of civil partnership legislation was a better way to address concerns raised by the LGBT community.
“The Evangelical Alliance supports marriage between a man and woman as it’s understood in the majority of countries around the world,” he said.
“If the latest motion in Stormont is really about equality then we are happy to have a discussion about how you fix the civil partnership legislation - we think that’s the way to do it.
“But the reality is in a democratic society that we live in we have had four votes, all of which have been won democratically, and really we think there are plenty more things we should be looking at rather than another vote on this issue.”
But Amnesty International’s Patrick Corrigan expressed the hope a majority of MLAs would vote in favour of same-sex marriage.
“I am hopeful that today will see a majority of MLAs vote in favour of marriage equality for first time, slowly catching up with where public opinion has already been for some years,” he said.
“However, the misuse of the petition of concern to hold back rather than uphold the rights of a minority group, will mean that the motion is formally defeated.
“It is a tragedy that same-sex couples are forced to ask the courts to fulfil a responsibility which has been abdicated for too long by too many politicians.”