Sinn Féin President Mary-Lou McDonald has called for an early Stormont election, insisting her party will not facilitate Northern Ireland "staggering on" without a functioning Executive.
She was speaking alongside ministers Michelle O'Neill and Conor Murphy as First Minister Paul Givan announced his resignation as part of a protest at the Northern Ireland Protocol.
Ms McDonald said in the absence of a functioning executive, an early election "must be called and the people must have their say".
"This ruse by the DUP to ratchet up tension and pressure in an ill-conceived attempt to get rid of the Protocol will not succeed, the Protocol is necessary, the changes or adaptations that are required to it, that work will be done through the Joint Committee, but for us ultimately, the people will finally be the arbiters and the decision makers in all of these regards," she said.
Ms O'Neill said she spoke to Mr Givan "very briefly" on the phone on Thursday.
She said her message to him in private was the same as Sinn Fein's in public - that the DUP's actions are a "deliberate act of harm against wider society".
Ms McDonald said: "This is one of those defining moments. We can do so much better than this chaotic theatre. Powersharing can work, but it can only work if parties involved are committed to it.
"Good government can deliver, of that there is no doubt. And that is what we, and we believe the other parties, wants to see happening.
"So if today's behaviour and decisions of the DUP show anything, it is again demonstrable evidence that we live in a time for real change, and this includes the prospect of constitutional change, as set out in the Good Friday Agreement."
It had been hoped to be pass a number of major pieces of legislation, including a three-year Stormont budget, a Climate Change Bill and a Bill on organ donation, before the Assembly was due to be dissolved at the end of March.
Ms McDonald said the situation is a "disgrace" when crucial legislation needs to be passed.
"The DUP actions have consequences, real consequences, for people struggling with the cost of living, consequences for businesses trying to rebuild after Covid, consequences for our health service, for waiting lists," she said.
"And it is a matter of disgrace that the budget now won't be passed and that investment in services such as cancer care and mental health are now in serious jeopardy."
Ms O'Neill said she has been in contact with other party leaders to meet to discuss the outstanding legislation.
"It's very clear there are catastrophic impacts in terms of the DUP's action today and there are many many casualties as a result of their political opportunism," she said.
"I have approached other party leaders, we need to work at pace to deliver on the rest of the legislation, things like the organ donation Bill that we want to see delivered upon."