Senior ministers are set for a showdown on Britain’s future relationship with the EU amid growing public tensions between Theresa May and David Davis.
It comes amid unconfirmed reports that Mr Davis, the Brexit Secretary, could resign over the issue.
Responding to the rumours, a Government source said: "He's a very senior member of the Cabinet. We really value his contribution."
With the inner Brexit war Cabinet set to meet on Thursday, the Government still could not say when the proposals would be made public.
Cabinet tensions on the backstop initiative emerged after Mr Davis was believed to be insisting that the UK should be able to unilaterally withdraw from any border agreement to maintain leverage with Brussels in negotiations.
When pressed on whether he could remain in post if the backstop deal did not meet his full approval, Mr Davis said: "That's a question I think for the Prime Minister to be honest."
Mr Davis made it clear that the document would be "decisive" as he said he planned to meet chief EU negotiator Michel Barnier again for Brexit talks next week.
Brexiteers accused Mrs May of giving the document regarding Northern Ireland to Cabinet supporters before hardline advocates of EU withdrawal Boris Johnson, according to The Times.
The Cabinet wrangling came as Mrs May faced a battle on a second front as she tried to persuade Tory rebels not to go against her when the EU (Withdrawal) Bill returns to the Commons on Tuesday.
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Mrs May is determined to try and stop Tory MPs inflicting humiliating defeats on her by siding with amendments backed by the House of Lords.
The Brexit Secretary is set to return to Brussels next week for talks with the EU's chief negotiator Michel Barnier.
Asked if Mr Davis had threatened to resign over the backstop issue, the Prime Minister's official spokesman replied: "Not that I'm aware of, no."
The return of the EU (Withdrawal) Bill to the Commons after a series of bruising defeats in the Lords poses another headache for the Prime Minister.
With Tory rebels set to side with Labour over measures aimed at keeping a customs union on the table, Mrs May engaged in crisis talks to avert a damaging defeat.
The move follows criticism of the original plan to rush the legislation through.
Other contentious pieces of legislation - the Trade Bill and the Taxation (Cross-border) Trade Bill - will also return to the Commons before the summer.
The Prime Minister's hopes of avoiding defeat over another amendment, aimed at keeping the UK in the single market, were given a boost as it emerged Labour MPs would be told to abstain.
But rebel MPs from both sides of the House of Commons are still pushing for a Norway-style Brexit agreement.
