The Irish border question must be clarified by this summer, the SDLP leader has said.
Any hardening of the frontier will be a deliberate violation of Northern Ireland's political process by the British Government, Colum Eastwood added.
He addressed party members at the SDLP annual conference at Titanic Belfast and urged another New Ireland Forum amid change caused by Brexit, saying: "The Irish Government must know that we need full clarity on the border this side of the summer.
"We can't let it slip until the EU Council meeting in October.
The backstop means in the absence of another solution, regulations relating to North-South matters - like the all-island economy - would continue to be aligned with the EU after Brexit in a year's time.
It was part of a December blueprint agreed between the British Government and the EU.
The border is the subject of intense discussion at official level in Brussels after the EU agreed to go on to discuss transitional arrangements in the Brexit negotiations.
Mr Eastwood added: "The only people who will actually end up delivering that backstop are the hardened Brexiteers who are determined to inflict economic self-harm.
He said the Good Friday Agreement which instituted north/south arrangements was sovereign, adding: "That Agreement belongs to the people of Ireland and we are only people with the right to change it.
"There are increasing numbers of politicians on both islands carelessly queuing up to rip it apart.
"We cannot and we will not allow it."
Mr Eastwood said the Good Friday Agreement had come of age, and told the crowd: "If Good Friday 20 years ago was to be the final destination of slow learners - let us not allow it to fall victim to fast wreckers.
"The choice remains the same.
"In time, when we are forced to look history full in the eye, let us not say that we narrowed our minds and thus narrowed the horizon.
"Let us instead say that we acted with courage, generosity and vision."
- Digital Desk and Press Association