Veteran Ulster Unionist MEP Jim Nicholson has warned the European Union that interfering in Northern Ireland politics would be a "serious mistake to make".
r Nicholson spoke out after European leaders gave the nod to a post-Brexit Northern Ireland re-joining the EU in the event of a united Ireland.
However, even Taoiseach Enda Kenny, who sought the assurance from the European Council, has admitted that will not happen any time soon.
The Taoiseach had requested clarification on the EU's position on Northern Ireland at Saturday's European Council Summit, attended by the leaders of the 27 remaining member states.
Mr Nicholson accused EU leaders of trying to make life difficult for the UK.
"Quite clearly I can smell the deft hand of the Department of Foreign Affairs of the government of the Republic of Ireland trying to play politics with Northern Ireland," he said.
"But the truth is, at the end of the day, the people of Northern Ireland will decide what their future is, not Dublin and certainly not Brussels."
"Europe has been good, they have never taken any sides in the Northern Ireland position and they have always supported Northern Ireland through the Peace programme. That should not be forgotten and we should thank Europe for that.
"But if they want to get involved in Northern Ireland's internal affairs, that would be a different matter and that would be a very serious mistake for them to make."
Taoiseach Enda Kenny said the decision from the EU leaders cleared up some doubts, but did not bring a united Ireland vote any closer.
He added: "Let me be clear, this is not about triggering any mechanism (for a vote). I have been very consistent in my view that the conditions for a referendum do not currently exist.
"But acknowledging the principle of the potential within the Good Friday Agreement (for unification) is hugely important."
However, DUP MP Ian Paisley was dismissive of the move.
He claimed the decision fell "into a hypothetical fantasy politics point of view - what would happen if?"
"The fact of the matter is, if there were a border poll, people would know they are voting to leave the United Kingdom and go into a Europe that could not pay for Northern Ireland," Mr Paisley said.
DUP MEP Diane Dodds added: "Maybe Enda Kenny wants to see a legacy, but quite frankly he should concentrate on his own affairs."
She dismissed suggestions that Brexit had pushed the unification debate into the political mainstream as "Sinn Fein propaganda". "The vast and overwhelming majority of people in Northern Ireland, from all persuasions, actually believe that the union that matters is the union with the United Kingdom," Mrs Dodds claimed.
Sinn Fein president Gerry Adams welcomed the move "to seamlessly resume full status with the EU following of a successful Irish unity referendum", saying that the "Good Friday Agreement provided for a pathway to Irish unity".
"However, it is disappointing and deeply concerning that even at the first hurdle the Irish government has fallen short," Mr Adams added.
"The EU Council guidelines fail to go far enough. They do not even match those agreed by the EU Parliament.
"If the Irish government fails to secure a better deal for Ireland during the actual negotiations, the implications for the economy and Good Friday Agreement will be profound."
However, Ulster Unionist MLA Doug Beattie, said: "Sinn Fein jumping up and down about the negotiating guidelines agreed at the EU-27 summit has a whiff of desperation about it.
"Northern Ireland's constitutional status has not changed and Enda Kenny has said that his view is that the conditions for a referendum do not currently exist.
"The Ulster Unionist Party has been clear that the focus should be on ensuring that the United Kingdom, and within that Northern Ireland, gets the best deal possible through the UK Government's negotiations with the EU.
"It is sad that some are opportunistically using Brexit to try and unpick the Union.
"The Belfast Agreement put the future of Northern Ireland in the hands of the people of Northern Ireland through the principle of consent.
"Sinn Fein should reflect on that when they talk about protecting the Belfast Agreement.
"They can try and claim a win, but these guidelines do not change the fact that Northern Ireland will remain a part of the United Kingdom while the majority of our citizens wish that to be the case."