DUP leader Sir Jeffrey Donaldson is to tell the top EU negotiator that it is decision time in talks about the Northern Ireland Protocol.
Sir Jeffrey is set to meet European Commission vice president Maros Sefcovic later.
In a statement ahead of the meeting, Sir Jeffrey said he will make it clear that his party’s continued participation in the Stormont Assembly is “not sustainable in the absence of action to remove the Irish Sea border”.
Unionist parties in Northern Ireland have called for action over the protocol which places additional checks on goods arriving from Great Britain.
It was designed to prevent a hard border being imposed in Ireland following the UK’s departure from the European Union.
UK Brexit minister Lord Frost has been engaged in talks with Mr Sefcovic.
Sir Jeffrey has claimed the EU is being “intransigent”.
“In a week in which the UK Government extended free unfettered access for goods moving from the Irish Republic to Great Britain, the intransigence of the European Union must now come to an end,” he said.
“I have shown respect and goodwill by giving space for the current talks to succeed, but regrettably this has not been reciprocated.”
“Mr Sefcovic will be left in no doubt, that the continued participation in the political institutions is not sustainable, in the absence of action to remove the Irish Sea Border.
“A small window of opportunity currently exists to begin the process of restoring Northern Ireland’s place within the UK’s Internal Market.
“If the European Union wish to protect the political institutions in Northern Ireland, then they must seize this opportunity.
“Failure to do so, will lead to the inevitable consequences which I outlined on September 9.
“It is now decision time for the EU.
“The time for talking is now over.
“Matters must now be brought to a head.”