Stormont has been plunged into a fresh crisis after unionists joined forces to warn of an action plan to protest against the ban on a Twelfth Orange Order return parade through Ardoyne.
Fears that the power-sharing institutions could be under threat increased when the DUP and Ulster Unionists also walked out of renewed talks on parades, flags and the past after one day.
And tensions escalated last night when it emerged the DUP had pulled out of a planned North South Ministerial Council meeting due to take place today.
Within minutes of the Parades Commission reaffirming last year's ban, a bombshell statement also signed by the TUV, the UVF-linked PUP and UDA-linked UPRG said a "graduated" unionist response would also involve the Orange Order and "peaceful and lawful protests".
The London Government immediately said the last thing Northern Ireland needed was another barrage of street demonstrations and violence.
Secretary of State Theresa Villiers warned against any public disorder which could undermine efforts to attract investment and damage Northern Ireland's image abroad.
Even before the DUP pulled out of today's cross-border talks, Deputy First Minister Martin McGuinness demanded clarification that the joint statement did not amount to a threat to collapse the Assembly and Executive.
"This is clear evidence that the Orange Order is now setting the pace for political unionism and the DUP in particular is now dancing to its tune," he said
Sinn Fein president Gerry Adams said it amounted to evidence of the unionist parties' failure to "stand firm" against demands of the Order and loyalist paramilitaries, and said both London and Dublin could not stand idly by.
"In the absence of all-party talks the onus now shifts very firmly to the two governments," he said.
"As co-equal guarantors of the Good Friday Agreement they must ensure continuing progress, and this has to include implementing agreements already made that are their sole responsibility." But Mrs Villiers made clear: "Ultimately, the only way to make lasting progress on resolving the contentious issues of flags, parading and the past has to be through renewed dialogue between Northern Ireland's political leadership.
"The Government will continue to do all we can to encourage an early resumption of these talks."
The unionist statement branded the revived Stormont talks, which had been due to continue into next week, as "fruitless".
The parties said they saw no more value in contact with the Parades Commission.
"The message the Parades Commission has sent out is simple," it said.
"It has shown that the commission members place no value on a relationship with unionism and have treated our advice with contempt.
"It has turned its face away from the evidence, including from the PSNI.
"It is regrettable, but so be it."
DUP deputy leader Nigel Dodds said: "It is vital everyone who is justifiably angry remains peaceful and stays within the law.
"Everyone should channel their energies into the graduated response outlined by the combined leadership of unionism."
And UUP MLA Michael Copeland said on Facebook: "We have, for some time, been aware that such an absurd parades determination would bring with it a very real risk of widespread violence and disorder."
TUV leader Jim Allister said: "We made clear there should be political consequences if the north Belfast situation was not resolved and specifically we made the point that while there was once a cry of 'No talk, no walk', the unionist response should be 'No walk, no talk'."
But SDLP leader Alasdair McDonnell appealed for people to take a step back.
"There is now a desperate need for people to keep calm and provide leadership," he said.
"Being difficult and being angry is not going to help anyone," he added.