Sinn Fein deputy leader Michelle O'Neill has said a no-deal Brexit is incompatible with the Good Friday Agreement and if it occurs then a referendum on Irish unity offers the only solution.
Speaking at a public debate at the Labour Party conference in Brighton, Mrs O'Neill said a no-deal Brexit will "inevitably" lead to the break-up of the United Kingdom.
"A no-deal Brexit and the Good Friday Agreement are mutually incompatible. It's as simple as that," Mrs O'Neill said.
"There is a deal on the table and it includes the Irish backstop, which must be maintained as an insurance policy and guarantee to protect peace, jobs and the all-Ireland economy and structures.
"In the event of a no-deal Brexit, however, a referendum on a united Ireland is an obvious option which must be on the table.
"There is a growing sense that circumstances are now rapidly changing which will inevitably lead to the final break-up of the current constitutional structures.
"People from across this society, even those of a British identity, are now seriously questioning whether there are any merits of staying within the Union after Brexit.
"The Good Friday Agreement provides a peaceful, democratic pathway to Irish unity.
"The issue of Irish unity has taken on a new dynamic because of Brexit. This cannot be ignored. The political momentum is moving in that direction.
"The EU has said in the event of Irish reunification the North would automatically rejoin the EU.
"People are coming to the Irish unity conversation not to become republicans and nationalists, but to remain Europeans - and the opportunity to stay in the European Union, through separation from Britain."
She added: "It can no longer be dismissed as a pipe-dream.
"Not only is this possible, but it is inevitable in the time ahead."
Meanwhile, Sinn Fein has indicated it is "open to an arrangement" between pro-Remain parties to oust DUP MPs.
Assembly Member Conor Murphy made the comment as John Finucane was selected to contest North Belfast in the event of a general election.
The Newry and Armagh representative said they expect an election to be called before Christmas, and said his party is "open" to an arrangement between pro-Remain parties here to unseat DUP MPs.
Mr Finucane told yesterday's selection meeting at Belfast Castle that it had the potential to be a "historic election" for Sinn Fein, and described North Belfast as a "key battlefield".
Mr Murphy urged co-operation between parties to send a pro-Remain message to Westminster. "There is only one candidate can win this seat from Nigel Dodds, and that is John Finucane," he said.
Mr Finucane said North Belfast represents an "opportunity to strike an almighty blow against Brexit by unseating an arch DUP Tory Brexiteer".
"The numbers are there to make this happen, we can win this seat.
"This election has the potential to be a historic one for us and North Belfast is a key battlefield."
DUP MP Gregory Campbell accused Sinn Fein of "begging for electoral pacts" and "running scared of the people". He added: "Remain coalition or not - voting DUP matters and voting DUP delivers."