UK and EU officials have agreed the draft text of a Brexit agreement in a significant breakthrough for the talks.
A cabinet source told the BBC that the document has been agreed at a technical level by officials from both sides after intensive discussions this week.
A special cabinet meeting will be held at 14:00 GMT on Wednesday as Theresa May seeks ministers' backing.
The prime minister is currently meeting ministers for one-to-one talks as they are given sight of the draft agreement.
Health Secretary Matt Hancock, Transport Secretary Chris Grayling and Chief Whip Julian Smith are among those who have been seen entering Downing Street.
Scottish Secretary David Mundell said he had yet to see the detail but he was "encouraged" by the progress made.
But leading Brexiteers, such as Boris Johnson and Jacob Rees-Mogg, have urged the cabinet to reject the draft agreement - which includes commitments over citizens' rights after Brexit, a proposed 21-month transition period after the UK's departure on 29 March 2019 and details of the so-called £39bn "divorce bill".
The future of the border between Northern Ireland and the Republic of Ireland has been the last major outstanding issue to be settled amid disagreements over how to guarantee that there will not be physical checks reintroduced after Brexit.
Cabinet ministers were briefed on the state of the negotiations earlier on Tuesday, when they were told a "small number of outstanding issues" remained to be sorted.
No 10 said ministers were now being called to a special meeting to "consider the draft agreement the negotiating teams have reached in Brussels, and to decide on next steps".
Before they do so, they will be able to read relevant "documentation".
The BBC's chief political correspondent Vicki Young said some ministers had "deep concerns" about the shape of the likely agreement, which critics say could leave the UK trapped in a customs agreement with the EU.
She said they would have to decide whether they could support it, and if not, whether to resign from cabinet.
Leading Brexiteers have already condemned the draft agreement, Boris Johnson saying it would see the UK remain in the customs union and "large parts" of the single market.
He told the BBC it was "utterly unacceptable to anyone who believes in democracy". "Am I going to vote against it. The answer is yes," he added.
And Labour leader Jeremy Corbyn said "given the shambolic nature of the negotiations, this is unlikely to be the good deal for the country".
'Failure to deliver'
Both the UK and EU want to schedule a special summit of European leaders at the end of November to sign off the reportedly 500 page withdrawal deal and the much shorter outline declaration of their future relationship.
Brussels has insisted it would only agree to put the wheels in motion for the summit if agreement can be reached on the issue of the Irish border.
Ambassadors from the remaining 27 EU states will meet in Brussels on Wednesday.
If a deal is agreed with the EU, Mrs May then needs to persuade her party - and the rest of Parliament - to support it in a key Commons vote.
Conservative Brexiteer Jacob Rees-Mogg said if details of the text reported by Irish broadcaster RTE were true, the UK would become a "vassal state" with Northern Ireland "being ruled from Dublin".
Such an agreement "failed to deliver on Brexit" and the cabinet should reject it, he told the BBC.
"I think what we know of this deal is deeply unsatisfactory," he said. "There seems to be growing opposition to these very poor proposals."
Meanwhile, following pressure from all sides of the Commons, ministers have agreed to provide MPs with a legal assessment of the implications for the UK of the Irish backstop and other controversial aspects of any deal.
Cabinet Office minister David Lidington said Attorney General Geoffrey Cox would make a statement to MPs and take questions ahead of the final vote on any Brexit deal.
MPs, he said, would get to see "a full reasoned position statement laying out the government's both political and also legal position on the proposed withdrawal agreement".
The Democratic Unionists' Westminster leader Nigel Dodds said he was pleased Parliament had "asserted its will" as it was imperative that all parties to the deal were clear in what way and for how long it would "legally bind" the UK.