Sinn Féin leader Mary Lou McDonald has rejected Peter Robinson's comments about a potential border poll.
The ex-DUP leader argued there could be chaos if a united Ireland was voted for in a border poll by 50% of voters plus one, but Ms McDonald denied this.
"What's sauce for the goose is sauce for the gander," said Ms McDonald.
"Partition is maintained on the basis of 50% plus one and then constitutional change and a new Ireland is ushered in on that basis - that's democracy."
Mr Robinson was not in attendance at a political leaders' debate at west Belfast festival Féile an Phobail.
The debate was attended by seven political figures from across Ireland.
Robin Swann (UUP); Stephen Farry (Alliance); Colum Eastwood (SDLP); Simon Hamilton (DUP); Mary Lou McDonald (Sinn Féin); Simon Harris (Fine Gael) and Lisa Chambers (Fianna Fáil) all sat on the panel.
Fianna Fáil's Lisa Chambers said that if nationalists won a border poll using the current mechanism "peace would not be preserved".
When asked if she would consider any change to the 50% plus one system, Ms McDonald said no.
She also said she accepted British identity and that people who are British in Northern Ireland would still be British in a united Ireland.
But DUP MLA Simon Hamilton accused Sinn Féin of not showing respect for British identity in Northern Ireland.
Alliance's Stephen Farry, who filled in for party leader Naomi Long, said Brexit had been destabilising and that a border poll was probably inevitable.
UUP leader Robin Swann argued that the focus on such a referendum was a distraction from the need to restore Stormont, a sentiment echoed by Mr Hamilton.
Before leaving the debate at St Mary's University Belfast early to catch a flight, Mr Swann he expressed his belief that Stormont could be restored if all parties - not just Sinn Féin and the DUP - were given roles in talks.
He said Northern Ireland Secretary Karen Bradley told him she did not have any plans for talks on restoring power at Stormont.
The SDLP's Colum Eastwood said he did not believe there should be a border poll until after Brexit, while Fine Gael's Simon Harris said creating a new Ireland before restoring Stormont was missing the point.