The Taoiseach Leo Varadkar has said the DUP does not want the best of both worlds for Northern Ireland.
He was speaking at a Dáil debate on the proposed Brexit text negotiated between the EU and UK.
The Dáil is debating the draft agreement, which was backed by the British cabinet last week.
It comes as British Prime Minister Theresa May held talks with European Commission President Jean-Claude Juncker in Brussels.
At the start of the debate, Mr Varadkar hit out at the DUP - which is propping up British Prime Minister Theresa May's Westminster government.
He said trying to argue with DUP leader Arlene Foster that this deal is the best one for Northern Ireland is not going to work.
"But that totally misunderstands her view - it's not the best of both worlds that the DUP wants.
"The DUP holds very firm to this view that the most important thing is the integrity of the United Kingdom, the integrity of the precious union.
"And if that means a lesser-world, that's acceptable - provided that the integrity of the union is upheld".
Mrs Foster and her party have called on Mrs May to re-negotiate the draft deal.
This is something Mr Varadkar said last week would not be possible, given the timeframe involved.
'Preparing for a no-deal scenario'
Tánaiste Simon Coveney speaking at the Fine Gael Ard Fheis in Dublin | Image: Sam Boal/RollingNews.ie
Meanwhile Tánaiste Simon Coveney has said the Government is continuing to prepare for a no-deal Brexit scenario from the UK.
Mr Coveney said the Government is hoping for a good outcome and "the closest possible partnership" from the end of March next year.
But he added: "The Government... continues to advance extensive and detailed Brexit preparedness and contingency work across all departments and State agencies.
"This addresses the full range of Brexit scenarios - to make sure Ireland is ready no matter what and come what may.
"The Government has focused on preparedness measures needed on an East-West basis, preparing our ports and airports.
"The first phase of a recruitment programme of approximately 1,000 staff, for customs and SPS controls, in addition to ICT and infrastructure measures is underway.
"This initial phase of recruitment will see staff in place by the end of March next year."
"Ignorant and clownish" behaviour
Fianna Fáil leader Micheal Martin arriving for the inauguration of Michael D Higgins as President of Ireland at Dublin Castle | Image: Eamonn Farrell/RollingNews.ie
Fianna Fáil leader Micheál Martin hit out at some Brexiteers, accusing them of showing "ignorant and clownish" behaviour.
He told the Dáil: "A fully agreed and ratified withdrawal treaty will be, at best, the end of the beginning.
"We will still face potentially years of negotiations and damaging uncertainty.
"As we saw last year, over-emphasising interim agreements, however welcome they may be, breeds a damaging complacency.
"It serves no useful purpose for us to waste our time here commenting on the ignorant and clownish behaviour of some Brexiteers.
"In meetings in different contexts I have experienced the Brexit advocacy of certain of the loudest Tory Europhobes.
"It is clear that they have no interest in rational discussion. Just like fundamentalists of all varieties, the more their ignorance is exposed the more fanatical they are in their advocacy.
"I would go as far as to say that we have as a country spent too much time in the past two years feeling indignant about the dishonesty and ignorance of many Brexiteers.
"Some of this time and space would have been better spent on a more questioning approach to our national preparations for Brexit.
"There is simply no way of looking at the hard facts of preparations and missing the gap between the rhetoric and the reality."
But he praised the draft deal: "It appears to us to be a balanced text where the union's negotiators went to the very limit of their mandate in order to show flexibility and to help London address its self-imposed pre-conditions.
"They did this in a highly professional and creative way."
Additional reporting: Sean Defoe
