Sinn Fein vice president Michelle O'Neill has said that the DUP "live in a fairytale world" over Brexit.
Mrs O'Neill was speaking following the defeat of Prime Minister Theresa May's Brexit withdrawal agreement in the House of Commons on Tuesday.
The DUP voted against Mrs May's deal due to concerns surrounding the backstop, which aims to prevent a hard border in Ireland after Brexit.
Despite the vote, the DUP are set to back Mrs May in a no-confidence motion against her government on Wednesday evening.
DUP leader Arlene Foster has repeatedly urged the Prime Minister to return to EU leaders and renegotiate to secure a "better deal".
However, Irish Foreign Minister Simon Coveney said that the EU leaders were in "no mood" to renegotiate the UK's exit deal.
“I don’t think the EU is in any mood to change the Withdrawal Agreement significantly at all,” the Tanaiste said.
“We don’t even know what the ask is, we’ll have to wait and see what they’re asking for.
“Those who have rejected the backstop do not have alternative solutions in terms of how we provide reassurance (on the border).”
Speaking on Twitter, Sinn Fein's O'Neill said that the DUP were "losing the run of themselves".
"It is crystal clear the DUP live in a fairytale world, thinking there is a deal without a backstop," the Mid Ulster MLA said.
"They are happy to sacrifice the interests of business and people in the north to deliver their hard Brexit - as usual the DUP are losing the run of themselves."