It comes as the deadline looms for a deal between London and Brussels.
British and European Union negotiators making headway on the Irish border hope for a Brexit deal breakthrough on Monday, diplomats said, though the British prime minister's Northern Ireland ally has stoked uncertainty by warning it could vote against her.
Downing Street insisted that defeat on the budget would not amount to a vote of no confidence in the Government under the terms of the legislation which provides for fixed-term, five-year parliaments.
Theresa May relies on DUP support in key votes because she does not have a majority in the House of Commons.
Among those due to attend today's War Cabinet are: the Prime Minister's effective deputy David Lidington; Jeremy Hunt, the Foreign Secretary; Sajid Javid, the Home Secretary; Liam Fox, the International Trade Secretary; Greg Clark, the Business Secretary; Michael Gove, the Environment Secretary, and Gavin Williamson, the Defence Secretary.
His constituency contains the port of Larne, identified by European Union chief Brexit negotiator Michel Barnier as a place where checks on animals and animal products from Great Britain into Northern Ireland could be intensified in order to prevent a hard border with the Republic of Ireland.
London hopes to resolve the issue with a future trade deal, but agrees there should be a "backstop" arrangement to avoid physical frontier checks until that deal is done.
Northern Ireland would also remain in the single market for goods.
Prized post-Brexit trade agreements with the United States, China and India would have only a "relatively modest" impact on Britain's economy, according to the government's official forecaster.
"They [the EU] said they think this is an incredible deal you are getting, something nobody else in the world has even been offered", said Seamus Leheny, the director of policy at the Freight Transport Association of Northern Ireland, who was at the meeting.
The DUP has 10 MPs, although Ian Paisley can not vote in the Commons until November 20 after being suspended for failing to declare two family holidays paid for by the Sri Lankan government.
"The DUP was always seen as the party of business, and if the business community says we need a backstop solution, maybe they think it will be harder for the DUP to block a deal", said Leheny.
Not such a pleasant morning for the Prime Minister who is trying to please the DUP, the European Research Group - the ultra pro-Brexit wing of her own party - and the EU.
Barnier said that the EU remained open to staying in a customs union with the whole of the United Kingdom, making a hard border unnecessary.