Tánaiste Simon Coveney has accused some British politicians of trying to unpick aspects of the Brexit withdrawal agreement.
The EU's chief Brexit negotiator Michel Barnier says that 90% of a deal with the UK is done.
However, Mr Barnier has warned the lack of progress on the Irish border issue could cause any deal to fail.
The issue of the backstop arrangement for Northern Ireland is still the main issue that can't be agreed.
Simon Coveney says the backstop has already been signed off on by the UK and that there can be no backtracking.
"Both sides have agreed as they go section by section, agreement by agreement, then those issues are settled and they move on," he said.
"In my view, not the British Prime Minister herself, but by others.
"We have to defend against that, because if we start that, we"ll never this done," he said.
Taoiseach Leo Varadkar said that it would be difficult for the EU to accept a deal in which the backstop would extend to all of the UK.
"We couldn't have a situation whereby the United Kingdom had access to the single market, which is our market, and at the same time was unable to undercut us in terms of standards, whether it was environmental standards, health, labour laws, State Aid, competition, and I don't think any country, or any union, would be able to accept that," he said.