Sinn Fein President Mary Lou McDonald has said that the UK Government are welcome to have their Brexit, but "they won’t take the North with them".
Mrs McDonald was speaking in Dublin on Saturday after the EU's Chief Negotiator Michel Barnier made a final offer to Prime Minister Theresa May on her Brexit deal.
Taking to Twitter on Thursday, Mr Barnier proposed that Britain could unilaterally leave the EU customs union, but said that Northern Ireland must remain as part of the backstop to prevent a hard border in Ireland.
The offer was quickly rejected by the DUP who said it was neither "realistic or sensible", while former Foreign Secretary Boris Johnston accused the EU of trying to "annex" Northern Ireland.
Mrs McDonald said that Sinn Fein's position was "consistent" with Mr Barnier's.
She accused the government of "playing down the clock, playing for time" and said that they had "absolute indifference to Ireland or Irish interests".
"If Britain wishes to Brexit who are we to stop them? But they won’t take the North with them and they’re not going to wreck the Irish economy and upend our peace process," the Sinn Fein leader said.
“That’s the bottom line. That’s a position that has been articulated at Irish Government level and by the European Parliament."
Mrs McDonald is set to travel to America next week for the annual St Patrick's Day celebrations. While there she will meeting with representatives of Irish America and US politicians to brief them on Brexit developments and the push for Irish unity.
“We will be asking them to stand with us in protecting the Good Friday Agreement and to join with us in reminding the British Government of their international obligations to Ireland in law, and that those obligations must be honoured," the Dublin Central TD said.
The Sinn Fein President said that the Irish Government needed to "hold firm" as Brexit negotiations enter their final stage and resist any pressure from London.
“Whether there is a deal or not the reality is that Brexit is bad for Ireland. Citizens in the North will be left behind."
Mrs May will put her withdrawal agreement to the House of Commons again on Tuesday in the hope of overturning the record 230-vote defeat she suffered in January.
Speaking on Friday she said that she needed "one more push" to get her deal through Parliament.