Fine Gael leadership contender Leo Varadkar has described Sinn Fein's demand for a border poll as "alarming", insisting a vote on Irish unity "at any point in the near future" would be counterproductive.
In a speech to Fine Gael members in Dublin-Rathdown, the Social Protection Minister also said that Fine Gael needed to take a "renewed interest" in the North.
He said he was "very concerned" that Sinn Fein might seek to "manipulate and exploit" recent developments to create division in both parts of the island, and build support North and South.
"The demand for a border poll is alarming," he said. "It is a return to a mindset in which a simple sectarian majority of 50pc plus one is enough to cause a change in the constitutional status of the North. It represents a mindset of: 'There's one more of us than you, so now we're in charge. It's our turn to dominate,'" he said.
A border poll held at any point in the near future would be "counterproductive," Mr Varadkar added. "While things may, and I think are likely, to change in the future, the result of such a poll now is likely to be a clear 'no' to a united Ireland," he said.
"Worse than that, such a campaign would polarise political opinion on both sides, making it more difficult to achieve the type of real co-operation... upon which a shared future can be built.
"I think we need to develop further the structures of co-operation and areas of working together, put in place or promised but not yet delivered, over the last 20 years."
Mr Varadkar added: "I believe in a united Ireland and would dearly love to see it occur in my lifetime. But before we have territorial unity, we must have unity among people.
"Bouncing Ulster Protestants into a unitary Irish state against their will would be as grievous a wrong as was abandoning a large Catholic minority in the North on partition. It could lead to alienation and even a return to violence. A unitary state formed on this basis would not be a good one."
In an important speech in Goatstown, he said he believed the country was entering a period when the importance of Northern Ireland to politics in the South would come to the fore again. "As a party, Fine Gael needs to see this and prepare for it," Mr Varadkar said.
Brexit, he added, would inevitably force the country to reassess its political relationship with the North and Britain as a whole. He also said Fine Gael should insist there would be no border again. A soft border comprised a camera on a pole, he said, and then the camera and the pole could become targets.
The minister said he did not think it possible for the North to have special status in the EU for as long as it remained part of the UK, but it could have special arrangements that allowed the status quo to remain in place.
The EU had shown itself to be "creative and pragmatic" when it came to other territories like Greenland, Andorra and the far-flung French overseas departments. "It can be creative and pragmatic as far as the island of Ireland is concerned," he added.
He said Fine Gael needed to reach out to persuade moderate unionists and middle-ground voters who support the Alliance and Green parties that "people who instinctively understood that Ulster farmers, businesses, students and security would be best served by such an arrangement".
He added: "Real lasting workable unity can only come about with a decent measure of support from both communities. It seems odd that those who have advocated for a shared future and co-operation should now seek to throw that away as they would try to ram through unity on a narrow simple majority basis.
"A broader approach based on persuasion, not on what birth rates might produce, would recognise that the destiny of the two communities in the North will always be intertwined and therefore require a shared future."