Michelle O’Neill has questioned the decision making of the Parades Commission and called on the Northern Ireland Secretary Sir Chris Bryant to intervene in the parade dispute.
Asked if she thought Stormont could collapse over Drumcree, she said: “The progress of the last 28 years have been brought into question by the actions of the Orange Order and those within political unionism that want to drag us backwards.
“What’s the point? What’s the point whenever people are going to railroad over their rights?”
Democratic Unionist Party (DUP) MP Carla Lockhart said the first minister was “whipping up hysteria” at an unlawful protest.
She called O’Neill’s comments “outrageous” and the protesters a “rabble”.
“The law is on our side,” she said.
“They’re afraid of 35 men, walking down a road silently.”
Prime Minister Andy Burnham has appealed for “calm on all sides”, saying there have been “big gains made in Northern Ireland, and we don’t want to see things go backwards”.
A spokesperson for the Irish government said: “Our primary concern remains to avoid a return to the divisions of the past, recalling the significant progress made over many years in furthering reconciliation under the Good Friday Agreement.”
Officers are operating checkpoints on the main roads into Portadown, and they are reporting a steady stream of vehicles arriving into the County Armagh town.
Drivers are being handed an information sheet, which says police will seek to facilitate peaceful protest where possible.