Democratic Unionist Party leader Jeffrey Donaldson has said the party's MPs will vote against a central element of the British government's deal with the EU on post-Brexit trade rules later this week.
Parliament will on Wednesday debate and vote on the so-called Stormont brake, a key part of the Windsor Framework agreement that enables Britain to stop new European Union laws from applying to goods in Northern Ireland if so requested by a third of Stormont MLAs.
In a statement, Mr Donaldson said: "Last week I indicated that while significant progress had been secured in the Windsor Framework across a number of areas it does not deal with some of the fundamental problems at the heart of our current difficulties.
"It is our party view that there remain key areas of concern which require further clarification, re-working and change as well as seeing further legal text.
"There is no doubt it is vital that the Northern Ireland Assembly must have at its disposal democratic mechanisms that are effective in law and which underscore the role of the locally elected representatives of the people of Northern Ireland to determine whether amended or new laws are implemented.
"Notwithstanding the issues and conditions which have to be met to make the brake work it remains the case that the "brake" is not designed for, and therefore cannot apply, to the EU law which is already in place and for which no consent has been given for its application.
"Whilst representing real progress the "brake" does not deal with the fundamental issue which is the imposition of EU law by the Protocol.
"Since the announcement that the "Stormont Brake" is to be debated and voted upon in Parliament on Wednesday there have been a number of indications that this vote will be read as indicative of current positions on the wider Windsor Framework package.
"Our Party Officers, the only decision-making mechanism in our party on these matters, met this morning and unanimously agreed that in the context of our ongoing concerns and the need to see further progress secured whilst continuing to seek clarification, change and re-working that our Members of Parliament would vote against the draft statutory instrument on Wednesday.
"We will continue to work with the government on all the outstanding issues relating to the Windsor Framework package to try to restore the delicate political balances within Northern Ireland and to seek to make further progress on all these matters."
Jeffrey Donaldson has been very careful to stress that this decision to vote against a key element of the Windsor Framework does not mean it has taken a definitive decision not to go back into power-sharing.
In a statement issued today and in subsequent interviews he spoke of the need for "further clarification", for "re-working and change", as well as the need to see details of the final legislation to implement what was agreed.
It is clear that many within his party have not been impressed by the hard sell from UK Prime Minister Rishi Sunak and still have concerns that Northern Ireland's constitutional position within the UK is being weakened.
Whatever business leaders say about the opportunities the deal can unlock, it is the political question about whether the same rules will apply in Belfast as in Bristol that will be the key area of debate within the party.
It is also clear that many within the party are nervous about walking away from devolution for good, and fearful that could cause more serious long term damage to the Union.
The Irish and British governments and the White House would all love US President Joe Biden to visit Northern Ireland with a fully functioning Stormont Executive up and running, or at the very least a strong indication that it's on the cards.
Jeffrey Donaldson has again made it clear that he will keep his cards close to his chest and will not be rushed into making a final decision, but he also knows the pressure will grow with each passing day.
Senior DUP MP Ian Paisley earlier said he would vote against the framework.
In an interview with the News Letter, Mr Paisley said: "I am categorically voting against, and I would be surprised if my colleagues do not join me".
He added: "My initial reaction to the Windsor Framework was that I didn't think it cut the mustard in terms of addressing our seven key tests (on restoring NI's place within the UK internal market).
"After taking time to study it and a least one legal opinion on it, and going through the details, and also having conversations and messages back and forward to the Secretary of State, I am still of that opinion - that it doesn't address any of our seven tests.
"It is the old substance dressed up in a new package with a ribbon around it, but it hasn't actually changed, or addressed the fundamental issue of Northern Ireland trade being disrupted in our internal UK market."
SDLP leader Colum Eastwood said that he is not surprised by the DUP's position.
He said that the main concerns of the DUP were checks and that they have been totally reduced.
Speaking to RTÉ's Drivetime, he said that "one of these days they (the DUP) are going to have to say yes" as in his view, the negotiating is done and there is "nothing more to get".
Mr Eastwood said it was "ridiculous" to give a full veto to 30 members of the Northern Ireland assembly for international EU regulations and that he did not understand the DUP's concerns.
