Rishi Sunak's new Brexit deal has been dealt a hammer blow after the DUP said it intends to vote against it.
Leader Sir Jeffrey Donaldson said party chiefs had unanimously agreed to oppose the Windsor Framework when it's put before MPs on Wednesday.
He said that while "real progress" has been made on Boris Johnson's botched Brexit agreement, it does not deal with the "fundamental issue" of imposition of EU law.
On Wednesday the Commons will be given a vote on the so-called Stormont brake, which gives the Northern Ireland assembly the power to object to EU law changes affecting the province.
Sir Jeffrey said in a statement: "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."
Sir Jeffrey said party officers this morning unanimously agreed to vote against the draft statutory instrument on Wednesday.
But he added that the DUP would "continue to work with the Government" to try to restore the "delicate political balances" in Northern Ireland.
No10 last week said the Stormont brake is at the "heart" of the Windsor Framework - but it is unclear which other aspects of the deal MPs will get to vote on in the future.
The agreement followed a complex round of negotiations aimed at undoing the worst excesses of Boris Johnson's deal, which caused devolved government to collapse in Northern Ireland.
It is likely Mr Sunak will also face opposition from within his own party.
Predictably Mr Johnson has been a thorn in Mr Sunak's side, saying he would "find it difficult to vote for something like this myself".
Mr Sunak has previously pledged that MPs will get their say, and his spokesman told reporters: "We said Parliament would have its say on the framework.
"This vote honours the Prime Minister’s commitment to provide MPs with the opportunity to vote on the new arrangements."
Downing Street insists the Windsor Framework deals with the main difficulties posed by the Northern Ireland Protocol.
It would allow the free flow of goods from Great Britain to Northern Ireland without the need for routine customs checks so long as they are not destined for the Republic.
The brake mechanism enables a minority of Stormont MLAs to formally flag concerns about the imposition of new EU laws in Northern Ireland - potentially leading to a UK Government veto.
In a speech laced with bitterness on March 2, Mr Johnson said: "This is not about the UK taking back control and although there are easements this is really a version of the solution that was being offered last year to Liz Truss when she was foreign secretary.
"This is the EU graciously unbending to allow us to do what we want to do in our own country, not by our laws, but by theirs."
And it's not clear if hardline Brexiteers within Tory ranks will be satisfied with what they've read.
The European Research Group of Tory Brexiteers has commissioned a so-called "star chamber" of experts to consider the deal before it decides how to vote.
Mark Francois, the group's chairman, said: "We are still awaiting the outcome of the star chamber's detailed legal audit of the Windsor Framework, which of course includes the Stormont brake.
"We now hope to see this completed before next Wednesday and members of the group will no doubt pay close attention to the star chamber's conclusions, prior to any vote."
But Labour has said it will support the government to get the deal through.
Keir Starmer told MPs last month that Labour would not "snipe" or "play political games". But he urged the latest Prime Minister to repay that faith by being "utterly unlike his predecessor".
