Governments on both sides of the Irish Sea will consider detail of the draft Brexit Withdrawal Agreement today.
The text has been agreed by officials - but faces a tough test as the UK Prime Minister Theresa May tries to rally domestic political support for it.
The Irish Cabinet is meeting to discuss the proposals at around 9:30am this morning.
Senior officials briefed the Taoiseach, the Tánaiste, the Minister for European Affairs and the Finance Minister on the proposals last night.
Later this afternoon, Mrs May will attempt to unite her Cabinet behind the plan – with a number of ministers understood to be sceptical.
It is just the first step for UK Prime Minister, who will spend the coming weeks attempting to muster enough support to get it through the House of Commons – with the DUP, arch-Brexiteers and some Remainers already making their opposition clear.
She summoned ministers to Downing Street one-by-one last night to read the proposed deal.
Cabinet sign-off is by no means assured – amid speculation that minister including Penny Mordaunt, Esther McVey and Liam Fox could be prepared to walk out if a deal ties the UK too closely to Brussels.
Ministers were given last night and this morning to consider the implications of the plan – although they were not permitted to bring the text home with them.
The Irish Government has said it wants to allow the UK Government time and space to consider the deal before commenting.
It is believed the UK Cabinet will have to sign off on the plan today if a special EU summit is to be called this month to finalise it.
EU leaders would be asked to rubber-stamp the plan – setting the stage for a crucial vote in the UK Parliament before Christmas.
Anger
Even before seeing the detail last night, Westminster MPs on both sides of the debate voiced strong opinions.
Speaking last night, the former UK Foreign Secretary Boris Johnson said he has been reading predictions about what's included in the agreement - and is horrified.
“If they are right then this is just about as bad as it could possibly be,” he said.
“What you have got is not only the UK remaining in the Customs Union forever and a day – so we can’t really do trade deals and we can’t take control of our laws – but we remain in regulatory alignment.”
The DUP set the stage for a Parliamentary showdown – effectively pulling its support for Mrs May and warning that “every vote will count” as she attempts to win the support of her Cabinet and the House of Commons.
It is not just Leave-supporting MPs who are unhappy however.
Remain backer Jo Johnson, who quit the government last week and called for a second referendum, told a People's Vote rally that his party would be "gravely imperilled if we are associated with this deal."
British Labour leader Jeremy Corbyn also said his party was likely to vote against the agreement if it is put to parliament.
"We will look at the details of what has been agreed when they are available," he said.
"But from what we know of the shambolic handling of these negotiations, this is unlikely to be a good deal for the country."
If the UK Cabinet agrees to support the plan, it will likely be published in full this evening.