The DUP leader has indicated that he intends to pull his ministers out of the Stormont Executive before November, if his demands on the Northern Ireland protocol are not met.
Jeffrey Donaldson also said he made the decision because he feared that negotiations between the EU and UK government over the protocol would be "dragged out" for years.
He has said that he wants the UK government to legislate in October to protect Northern Ireland’s place within the UK internal market and avoid a collapse of the powersharing institutions and an early election.
The DUP leader’s position, which was set out in a speech on Thursday, brought a furious reaction from other Stormont parties.
But speaking to the BBC Nolan Show on Friday, Mr Donaldson said he had been working on the strategy of opposition to the Northern Ireland protocol for months.
He said: “I have been reasonable, I have given people time to take the action that I feel is necessary to remove this Irish Sea border.
“I have worked with the government, I have engaged with the EU, I have put forward proposals and suggestions in terms of how we can address these issues.
“There reaches a point where, with the decision taken to extend the grace periods indefinitely, that it appears to me that this will be dragged out for months, if not years, and we simply can’t afford that.
“The harm that is being done to our economy every day is not sustainable.”
The protocol was agreed by the UK and EU as a way to maintain a free-flowing land border on the island of Ireland after Brexit.
It achieves that by moving many of the checks and processes required on goods to the Irish Sea.
Under the arrangements, Northern Ireland remains in the EU single market for goods and continues to apply EU customs rules.
Unionists in Northern Ireland have been vehemently opposed to its terms which see additional checks on goods arriving to the region from the rest of the UK.
Mr Donaldson said he expected the British government to protect Northern Ireland’s place in the UK internal market, pointing out that this was a commitment in the New Decade, New Approach agreement which restored Stormont after a three-year suspension.
Asked if he would pull his ministers out of the Executive before November if the government did not legislate in October, Mr Donaldson said: “I think that is the sort of timescale we are working to now.
“If they introduce legislation to give effect to the commitment they gave in the New Decade, New Approach agreement to protect our place in the UK internal market, to remove the Irish Sea border, I think that would be a very significant step indeed.”
Mr Donaldson met this week with the UK's Brexit minister, David Frost, and also with European Commission vice-president Maros Sefcovic and said he believes there is now a "realisation" that action needs to be taken over the protocol. - PA
