Concern has been raised that nobody from Northern Ireland has been present at talks with the EU's chief Brexit negotiator.
Michel Barnier held separate meetings on Thursday with the first ministers of Wales and Scotland, Carwyn Jones and Nicola Sturgeon, as well as Labour leader Jeremy Corbyn.
However, due to the collapse of the Stormont government, nobody from the region attended the talks.
SDLP leader Colum Eastwood warned that the Stormont Executive must be restored in order "to resist" the "catastrophe" of Brexit.
"The threat posed to this part of our island cannot be underestimated, we must restore the institutions to resist it. We cannot be left behind, it is our responsibility to prevent this catastrophe," said Mr Eastwood.
He added: "Today the North of Ireland is cut out of formal talks with the head negotiator Michel Barnier due to the absence of a government here.
"While Scotland and Wales meet with the EU lead, we are left without a voice at that table."
Mr Eastwood said that in Westminster Irish nationalism has been silenced by the refusal of Sinn Fein MPs to take their seats to fight the "destructive" Repeal Bill to convert EU law into British law.
He urged the two main parties, Sinn Fein and the DUP, to reach an agreement to restore the Stormont institutions.
He said: "I've said it before and I'll say it again, Brexit is the most dangerous economic, social and constitutional crisis to face this island since partition. It demands our immediate attention and our immediate response.
"We must return a system of sustainable devolution. The alternative is that we are dragged into direct rule, where the pro-Brexit Tories and DUP have a free hand on our futures.
"Those of us elected on mandates to fight a hard Brexit, must be able to do that."
DUP MP Jeffrey Donaldson has insisted his party is ready to go back into government, but warned that the region is facing a period of direct rule.
"Northern Ireland needs its voice represented in the Brexit negotiations. I call on Sinn Fein to abandon their policy of not allowing the Executive to be formed," he said.
"In the absence of an Executive we cannot continue with the political vacuum. Big decisions need to be taken, not least on spending.
"We need the Secretary of State very soon to publish his plans with how he intends to deal with the impasse. I think we are heading for a period of direct rule," he told BBC Radio Ulster.