Pro-gay marriage protests at Stormont and Derry
Separate protests have taken place as MLAs at Stormont are set to debate a Sinn Fein call for same-sex marriage to be legalised in Northern Ireland.
Pro-gay marriage protesters gathered at Stormont and in Londonderry.
The DUP has already indicated an intention to use a petition of concern, which is effectively a veto.
However, one of the protesters, John O'Doherty, chair of the equal marriage NI campaign, said they would keep trying until they succeeded.
A similar motion was defeated in the assembly last October.
Speaking at the protest at Guildhall Square in Derry, Eamon McCann said: "I think it's tremendously important that we highlight the continued oppression of gay and lesbian and bi- and transgendered people, particularly in a society where so much was made for so many years about the need for equality.
Meanwhile, Amnesty International has warned of a likely legal challenge if Northern Ireland is left as the only part of the UK without marriage rights for same-sex couples.
The DUP's petition of concern would ensure that the motion would need to command a cross-community majority to succeed.
Patrick Corrigan, Amnesty International's Northern Ireland programme director, said: "States may not discriminate with regards to the right to marry and found a family, on the basis of sexual orientation or gender identity.
"That obligation is clear in international law. This means that marriage should be available to same-sex couples in Northern Ireland just as it appears it soon will be in other parts of the UK.
"Should politicians fail to act, there could be a straightforward legal challenge on the basis of inferior treatment of same-sex couples in Northern Ireland with regards to the right to marry and found a family."
Mr Corrigan believes such a legal challenge seems likely and would appear to have strong grounds for success.
DUP Chief Whip Peter Weir confirmed the party has tabled a Petition of Concern on the motion, which has been tabled by Sinn Fein.
Mr Weir said: "It is only a few months since the assembly last debated this issue and views were clearly expressed at that time.
"It has been made very clear that same-sex marriage will not be introduced in Northern Ireland and the DUP is tabling a Petition of Concern to ensure that this motion will not be carried."