Following three days of talks with key figures in Brussels, DUP leader Arlene Foster said Mrs May could not in "good conscience" accept the proposals now on the table from the European Union.
He suggested all 10 DUP MPs could vote down this month's budget to "pull the government back into keeping its promises". She'd be ripping up her guarantee to support the PM in the commons. Instead, as Newsnight's Nick Watt reported last night, there's a new plan to insert a "review clause" for the backstop, rather than an end-date, into the UK's withdrawal agreement.
She added: "Brexit seems to be going ahead one way or the other".
"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.
He added: "It was a warning: "Don't take us for granted".
And she again rejected any suggestion the north should remain within the single market, accusing Brussels of wanting to "place an effective one-way turnstile from Northern Ireland into the rest of the United Kingdom". "If they haven't, there'll be consequences".
Theresa May has been put on notice by her allies in the Democratic Unionist Party to change course on Brexit or risk the collapse of her government.
"It's been wrong, and if she continues down the road that Michel Barnier wants her to she'll no longer have our support", he warned.
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. 'There would appear to be progress, but sometimes the devil is in the details, ' she said.
"That is not the best of both worlds".
It would give Northern Ireland businesses "unfettered access" to both the single market and Britain and is a "really big deal" for the European Union, according to those present.
"The only visible systematic checks between Northern Ireland and the rest of the United Kingdom would involve scanning the bar codes on lorries or containers, which should be done on ferries or in transit ports".
Mrs Clinton made her remarks during a visit to Queen's University, where she collected an honorary degree for her "considerable contribution to the Northern Ireland peace process".
The Northern Ireland Retail Consortium (NIRC), which was also at the meeting, said the deal on the table was uniquely beneficial to Northern Ireland's economy, which would suffer disproportionately from Brexit.