Sinon Fain's leader Mary Lou McDonald described the braxite deal as "the worst option".
Mrs McDonald said that most voters in Northern Ireland had opposed – it was "fundamentally wrong" and "democracy".
"It will restrict the economy, the contract and the rights of citizens," she said.
"The agreement between the EU 27 and the British Government does not resolve the breaks.
"It's the worst option – not a good brax."
Sien Fien's leader added, "It must be clear that the stiffness of the border in Ireland or the renunciation of Good Friday agreement will not be seen in any way."
Last week, writing in The Irish News, Miss McDonald's greeted nicely in the text a few days ago by British Prime Minister Theresa May, but said "there is still a need for concern and clarity".
"It (backstop) provides the following line and our insurance policy against Braxtil's worst exaggeration, which we know will be catastrophic for this country."
"Backstop is not perfect and neither is a withdrawal agreement."
Meanwhile, Sinn Féin MEP Martin Anderson did not accuse North Indians of voting in the European elections after North Breacet after Loosur Wurudkar.
The Republic has got two additional MEPs after the break, which will bring its total number 13, while the North will lose its current three seats.
M. Anderson told RTÉ: "The Irish government is one of the few member states that have deprived their citizens of voting rights that do not reside in member states – 22 other member states do this.
"The Irish government can do this on the shock of the pen if they want."