The DUP have blasted Boris Johnson for being "too eager" to get a deal and avoid a delay "at any cost".
Deputy leader Nigel Dodds made the remarks after his party refused to back the deal the PM has secured in Brussels.
He told ITV News: "In order to avoid an extension he has been too eager by far to get a deal at any cost.
“The fact of the matter is if he had held his nerve and held out he would of course got better concessions which kept the integrity of the UK."
Mr Johnson faces an uphill battle to get the deal backed during an extraordinary sitting of Parliament on Saturday, after his key and influential allies in the DUP rejected it.
Speaking at a press conference in Brussels, Mr Johnson appealed to those in Northern Ireland as well as across party lines in order to encourage support for the deal.
"I am very confident that when my colleagues in Parliament study this agreement that they will want to vote for it on Saturday and in succeeding days," he said.
"We've been at this now, as I say, for three and a half years. It hasn't always been an easy experience for the UK. It's been long, it's been painful, it's been divisive.
"And now is the moment for us as a country to come together. Now is the moment for our parliamentarians to come together and get this thing done."
Appealing to Arlene Foster's party, he insisted the country can leave the bloc "as one United Kingdom" and "decide our future together".
