Taoiseach Leo Varadkar downplayed the prospects of the European Union countenancing amendments to a text that has taken two years to develop.
Mr Irwin said NIFDA welcomes the draft withdrawal agreement as a positive development in the ongoing Brexit negotiations, and they would be hopeful that this will enable more substantive talks around a future trading relationship with the EU.
The so-called Northern Ireland backstop, which aims to keep the border between the British province and EU member Ireland open, would all but leave Northern Ireland inside the EU's single market if an eventual British/EU trade deal can not maintain the now frictionless frontier.
However, DUP MP Jeffrey Donaldson said he did not believe it was the best deal for Northern Ireland.
He said the draft agreement had fully spelt out the "backstop" arrangement that would apply in Ireland if a wider EU-UK trade deal fails to materialise.
Mr Varadkar said he did not think the draft agreement could be re-negotiated before the end of March and that "any renegotiation would involve postponing Brexit".
While Dublin has prepared and begun triggering contingency plans for changes to trade with mainland Britain, including the hiring of 1 000 customs officials, it has consistently said it will make no such plans for infrastructure on the land border.
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"I think it is very hard to start making amendments without everyone wanting to make amendments and you could see the whole thing unravel", he said.
"The Irish government could only ever seek to influence the process, they cannot manage the internal affairs of the Tory party", he said.
"Obviously if it's defeated in Westminster, it's hard to know where we go from there, as others have said it's maybe hard Brexit or no hard Brexit at all, but that's a decision for the UK Parliament to make".
And while there is widespread opposition to May's Brexit withdrawal deal now, that could ease "as reality kicks in, as the precipice approaches", Varadkar said.
"None of them solve the Irish border question".
An open border is a legacy of the 1998 Good Friday agreement, which ended fighting between the north's pro-British unionists and nationalists who favour a united Ireland.