DUP MP Sammy Wilson has warned that his party's confidence-and-supply deal to support the Conservative government could be withdrawn if Northern Ireland is treated differently to rest of the UK post-Brexit.
Speaking to the BBC, he said any attempt to "placate Dublin and the EU" could see the premature end of DUP support at Westminster.
A report in The Times claimed that British negotiators had put forward a proposal to devolve powers to Northern Ireland to enable "customs convergence" with the Republic in areas such as agriculture and energy in an attempt to break the deadlock.
The paper quoted sources in Dublin as saying that there had been "movement" on the issue and confidence was growing that agreement could be reached in time for next month's summit in Brussels.
But the East Antrim MP said that "if there is any hint that in order to placate Dublin and the EU, they're prepared to have Northern Ireland treated differently than the rest of the UK, then they can't rely on our vote".
He added: "They have to recognise that if this is about treating Northern Ireland differently, or leaving us half in the EU, dragging along behind regulations which change in Dublin, it's not on."
Mr Wilson's remarks come after DUP MP Ian Paisley accused the Dublin government of "disgraceful" behaviour in the Brexit negotiations.
"As early as September in 2019 they will need to make a fisheries deal, not with the rest of the EU, but with us, and, frankly, if they continue to exacerbate our will as citizens of the United Kingdom, I think we should make that fisheries deal extremely long, tenuous and hard for them," he said.
DUP Leader Arlene Foster issued a statement this afternoon reiterating her party's position that there can be no special arrangements for the north in any Brexit deal.
“The United Kingdom voted to the leave the European Union as one nation and we are leaving as one nation," she said.
"Her Majesty’s Government have a clear understanding that the DUP will not countenance any arrangement that could lead to a new border being created in the Irish Sea. Indeed, the Prime Minister has been categorical on this matter in the House of Commons.
The former first minister said "there can be no arrangements agreed that compromise the integrity of the UK single market" and place barriers, real or perceived, to the free movement of goods, services and capital between Northern Ireland and the rest of the United Kingdom."
The leaders of the remaining 27 EU states, including Taoiseach Leo Varadkar, have a veto on triggering the second phase of talks, meaning Mrs May must be sure of support from Dublin for progress to be made.
However, appearing on BBC2's Newsnight last night, Dublin's Agriculture Minister Michael Creed said they had yet to see a workable solution from the UK.
He said that having ruled out an Irish proposal for Northern Ireland to remain part of the single market and the customs union, it was up to the British to say how they could get round the need for border checks.
"If the UK has clearly said no to a single market and customs union, it is clearly incumbent on the British government to articulate a way forward that enables us to have an invisible, seamless border which they have said they want," he said.
"We need political solutions now and we are not getting them from the UK Government."
