Finance Minister Sammy Wilson has accused Sinn Fein of “behaving like IRA suspects” over the looming spending cuts.
The comment shows just how seriously party political infighting over the cuts has escalated at Stormont.
The row comes as First Ministers Peter Robinson and Martin McGuinness meet Chancellor George Osborne in London today to plead Northern Ireland’s case on the dangers of swingeing cutbacks here.
While they are over at Westminster putting on a united front, back at the Assembly there is growing friction between ministers and MLAs along party political lines.
This is raising fears that the Tories may see the disunity as an opportunity to bring in sweeping cuts in the face of a lack of any concerted opposition or agreement on how best to deal with the cuts.
SDLP MLA Alban Maginness, who chairs the Assembly's Enterprise Committee, launched a stinging attack on the DUP and Sinn Fein over the disagreements.
He said: “If the First and deputy First Ministers are so obviously and publicly divided, how on earth are they going to get a good deal from the British Exchequer or the British Prime Minister? It is well nigh impossible.
“It is just typical of these two parties — they can't agree on anything. They can't get agreement on parades, on education or on something as fundamental as the economy.”
Mr Wilson has now said his budget timetable may be delayed due to “a lack of co-operation by some Executive colleagues”.
In his latest and most pointed attack, he likened the party's position to IRA suspects staying silent during police questioning.
The Finance Minister said: “I think I now know the frustration the police officers who had to interview Sinn Fein members when they were taken into Castlereagh for questioning must have experienced.
“Attempts to engage them in discussions about their spending plans and how they intend to deal with the savings which their departments must find as a result of the budget cuts imposed by the Conservative/Liberal coalition have proved fruitless as they exercise their right to remain silent.”
At the Assembly yesterday, senior Sinn Fein MLA Pat Doherty alleged Mr Wilson had “acquiesced” in cuts.
DUP First Minister Peter Robinson retorted: “We all know that the Finance Minister has done nothing of the sort.
“He has attempted to bring some realism to the situation.”
Mr Wilson last week said he aimed to have the Executive's next budget ready for debate on the Assembly floor early in 2011, to cover a four-year period from next April. Public funding will be severely constrained in this period under the spending review statement to be made by Mr Osborne on October 20.
He stressed that public bodies need to have certainty as soon as possible on their funding from next April.
Alliance Finance spokesman Stephen Farry is also concerned. He said: “It is critical that the Executive gets its act together.”