The Republic of Ireland would become isolated if the UK left the European Union, the DUP claimed.
Irish concerns were motivated by fear of losing a major ally in Europe, East Belfast MP Gavin Robinson alleged.
He gave evidence to the Northern Ireland Affairs Committee of MPs about the impact of Brexit and said the Irish government had benefited through its relationship with the UK at Brussels.
“They are afraid of us leaving because they will lose their big friend in Europe.
“Their concern is more to do with losing their big mate in a big pool and that they will become quite isolated should we choose to leave.”
The committee is examining the potential impact of Brexit on Northern Ireland, including relations with the south. The DUP favours an exit and has previously minimised the impact for issues such as cross-border security.
Mr Robinson said there were common travel arrangements between Britain and Ireland before EU accession and there would be afterwards.
He attacked critics of Brexit who have warned it could jeopardise the peace process.
“I think that touches to a base level of politics, of concern and fear which I think is not suitable nor of a credit to anyone who should raise those.”
Sinn Fein Stormont MLA Megan Fearon said Ireland north and south was better in the EU.
“All sections of our society from agriculture, business, education and the community and voluntary sectors have received practical support, including funding, from Europe.
“The EU has also been a major supporter of the development of the peace and political processes over the last two decades.
“As an MLA representing a border area, I know only too well the negative impact of partition. That would only be reinforced with a new European border.
“Ireland, north and south is better in the European Union and we cannot allow policies directed from the south-east of England to change that.”
Following clashes with pro-Brexit Labour MP Kate Hoey, an SDLP committee member walked out.
Former party leader Dr Alasdair McDonnell called on the chairman to “control” his fellow member.