Guy Verhofstadt, the EU's Brexit co-ordinator, has said the European Parliament would fight for Northern Ireland to remain under EU law.
he leading MEP, speaking in the Constitutional Affairs Committee on Tuesday in Brussels, said it was the only way to prevent a hard border in Ireland and "guarantee the Good Friday Agreement".
“It’s for us key as parliament that there will be in future, whatever the outcome of negotiations will be, there is no divergence in norms, rules, standards between Northern Ireland and the Irish republic. That is our goal,” he said.
“That is the best way, in our point of view, to solve the problem, to guarantee the Good Friday Agreement and guarantee the Common Travel Area and guarantee no hardening of the border because of Brexit.”
The DUP described his proposals as disastrous saying it effectively cut Northern Ireland off from the rest of the UK.
DUP MEP Diane Dodds said: “I am not surprised but greatly disappointed by the comments from Guy Verhofstadt. They are neither imaginative nor progressive. Such an outcome would be constitutionally unacceptable and economically disastrous.
"For the EU 27 to effectively propose creating a border between Northern Ireland and the rest of the United Kingdom is reckless.
"Crucially for Northern Ireland businesses, there was a clear commitment that Northern Ireland would have “unfettered” access to and from the United Kingdom internal market.
"The Government should rightly reject those aspects which don't reflect the balance of the agreement already made between the EU and Her Majesty’s Government.
"Brussels negotiators have lectured the UK that there can be no cherry picking of the obligations and responsibilities of previous agreements however on this occasion it seems to be a case of ‘do as I say but not as I do’."
The UUP said the comments amounted to placing a border between the UK and Northern Ireland.
UUP MEP Jim Nicholson added: "Northern Ireland cannot afford to be separated from its most important market - the UK single market. Great Britain accounts for around 60% of all external sales."
He added: "Unionists will watch developments in the coming days and weeks with great interest. There are some who see Brexit as an opportunity to weaken Northern Ireland’s position in the United Kingdom. There are others who see cutting off Northern Ireland as a clean way to make Brexit easier.
“It is up to the Government to ensure it stands by its commitments that the integrity of the United Kingdom, and its own single market, will not be compromised.”