SDLP leader Colum Eastwood has said a Brexit represents the biggest immediate threat to the economy of Northern Ireland and to the island as a whole.
Speaking ahead of delivering a keynote address in Brussels on Thursday night at an event organised by the Party of European Socialists Mr Eastwood said any result in Northern Ireland should be respected separately from the rest of the UK result and that a Brexit would fundamentally undermine successive Anglo-Irish Agreements.
He also urged the Taoiseach Enda Kenny to stand by those Agreements when meeting the British Prime Minister David Cameron next week.
Mr Eastwood said: "It appears more and more likely that we will be faced with a ‘Brexit’ referendum this year, possibly as early as the summer.
"Tonight in Brussels I’ll be outlining the devastating impact that a ‘Brexit’ would have on Northern Ireland. A ‘Brexit’ is a threat to farming families, a threat to our business community and a threat to our exports. In the case of Northern Ireland it is also a threat to the multiple arrangements and Agreements between the islands of Ireland and Britain.
"There is a huge amount at stake. I will be meeting with the Taoiseach in Dublin on Saturday. I will urge him to represent the interests of the entire island, not just the 26 counties, when speaking with the British Prime Minister in Downing Street next week.
"A Brexit would undermine and destabilise the fabric of successive Anglo-Irish Agreements. It would undermine and destabilise our North-South institutions. It would resurrect borders and resurrect barriers for business.
"As co-guarantor of those Anglo-Irish Agreements, the Taoiseach has a role and a duty to represent the interests of the North on this issue.
“The selfish and sectional interests of some in the Tory party cannot be the only voice steering this decision and debate.
“The SDLP has a clear view on what should happen. We will be fighting for the referendum vote in the North to be respected separately.
“The vote of Northern Ireland citizens should be respected separately. After all, we have most to lose.”
Meanwhile the Northern Ireland Secretary Theresa Villiers has refused to be drawn on whether an EU exit would be good for Northern Ireland amid concerns over a split within her team at the Northern Ireland Office.
Ms Villiers is reported to be considering campaigning against the UK's continued membership of the European Union during the forthcoming referendum.
In contrast, Northern Ireland minister Ben Wallace told MPs he believed a reformed EU was "where the UK wants to be".
Labour urged Mr Wallace to reassure the Stormont Executive and Northern Irish public about the region's future within the EU given the "mixed messages" from him and his ministerial boss.
DUP MP Sammy Wilson tried to push Ms Villiers to back a British exit - referred to as Brexit - as he noted the positives of leaving.
The MP for East Antrim asked Ms Villiers: "While the devolution of corporation tax will be important in growing the Northern Ireland economy, would you also agree a vote to leave the EU would help the Northern Ireland economy insofar as it would release £18bn every year for expenditure on public services, would enable us to enter trade agreements with growing parts of the world, and would release us from the stifling bureaucracy of Europe?"
Ms Villiers replied: "Well, I'm afraid you're tempting me to engage in arguments which are rightly a matter for everyone in this country when they get to vote on that referendum.
"We promised a referendum in our manifesto - that's what we're going to deliver."
Margaret Ritchie MP earlier asked Mr Wallace: "Would you encourage your colleague (Ms Villiers) to argue for a yes vote in the EU referendum?"
Mr Wallace replied: "I think there's a temptation in front of me. I think what I'd say is, certainly up to date, membership of the European Union has been good for Northern Ireland. I hope and support the Prime Minister's efforts in achieving reform.
"A reformed EU is where the United Kingdom wants to be - an EU that works to the benefit of everyone in the United Kingdom - and I think if we can achieve that then we can take advantage of being neighbours of Ireland - one of the biggest economic partners of Northern Ireland - to make sure the economy can go from strength to strength."
Shadow Northern Ireland Secretary Vernon Coaker also warned there was "very real concern" in the region about the impact of leaving the EU on trade and investment.
He told the Northern Ireland minister: "You will know there's very serious concern in Northern Ireland about a possible Brexit, in particular because of the fact that it's the only part of the UK with a land border with another EU country.
"Can I also (press you) to reassure the Executive and the people of Northern Ireland about this in view of the mixed messages on Brexit emanating from the ministerial team - in particular your views as opposed to the secretary of state."
Mr Wallace replied: "There is no mixed message. Both myself and (Ms Villiers) are keen for the EU to produce some reforms, as is the Prime Minister's strategy. And when those reforms - and maybe you know what the EU is agreeing, maybe you have a special hotline - are presented to this House, then we'll be able to make a decision.
"For my part, I believe in the past that membership of the EU has been good for Northern Ireland."
David Cameron insisted he is "confident" the UK will remain in a reformed European Union if he gets the deal he is seeking for a new relationship with Brussels.
The Prime Minister said he is in "no hurry" to secure a deal on a package of reforms to Britain's EU membership at the upcoming Brussels summit in February but if an agreement is reached he will "sell it very hard" to the public ahead of the promised referendum.
A deal at the European Council of February 18-19 is widely seen as essential if Mr Cameron is to stage his in/out referendum before the summer.
Mr Cameron told ITV News: "A deal could be done in February, there is progress in each of the four areas I have identified and with goodwill I think we could get that deal.
"What I am saying very clearly is if there is a deal on the table, there will be no funny business from me, I will pick it up, I will take it to the British people and I will sell it very hard because it will be right for Britain.
"But if it isn't ready in February, if it isn't what I want, if it isn't what I want, if it isn't what is right for Britain, then we will need to take more time. Getting this right is more important than getting on with it."
In an interview with French broadcaster TF1 he denied his reform demands were an attempt to "blackmail" fellow EU leaders into agreeing to reforms instead of risking a British exit.
"No, I don't believe it is. I mean, we have raised the concerns we have over many years, and I set them out very clearly in my manifesto that I put in front of the British people. And I don't think the things we're asking for are unreasonable."
He acknowledged the referendum was a "huge responsibility" but "I think now, asking the British people to stay in a reformed Europe or leave, it's the right time to do that, particularly if we can achieve these changes on competitiveness, on political union, on the euro, on migration".
"If we achieve these things, then I'm confident we'll stay in a reformed Europe," he added.
Asked if he felt "deeply European", the Prime Minister replied: "Of course. Britain is a European country, and I feel very much part of that."
The Prime Minister was interviewed in Davos on the latest stage of his diplomatic offensive to build support for his reform demands before heading to Prague for talks on Friday.
In his speech at the World Economic Forum event he said he was ready to be "patient" in order to get the right result.
Securing a deal next month was "achievable (and) doable", he said. But he added: "We are certainly not there yet."
Britain's demands for change on the four issues of migration, sovereignty, competitiveness and protection for non-euro states were "not outrageous asks", but offered "a huge prize", he said.
Prospects for a swift agreement were played down by French prime minister Manuel Valls, who said the negotiations had "only just begun" and warned that a deal "at any price" would not be acceptable.
Mr Cameron held talks with Mr Valls at the Swiss ski resort, along with Dutch prime minister Mark Rutte and his counterpart from Luxembourg Xavier Bettel.
A Downing Street spokeswoman said: "In all three the PM discussed the UK's renegotiation of its membership of the EU. Everyone agreed the importance of maintaining momentum towards getting a deal done, noting that there was a good understanding of the main issues and that with hard work solutions could be found in all four areas."
Sweden's migration minister Morgan Johansson told Channel 4 News: "I think that the Prime Minister is playing a game with quite high stakes here.
"We will see where it ends up but I hope the UK will still be a part of the European Union."