DUP MP Ian Paisley sent a warning to Brexit negotiators in the Republic of Ireland not to "undermine our position and our sovereign integrity".
Mr Paisley is one of 10 DUP pro-Brexit MPs who are propping up the Government on key votes.
He told Irish broadcaster RTE: "If the Republic of Ireland is going to keep shouting at our border and telling us that it is all doom and gloom and we are not going to get a proper relationship, that interferes in the negotiation process.
"All of us, every constituent part, Northern Ireland, Scotland, Wales and England, are leaving the EU.
"Don't undermine our position and our sovereign integrity."
He added that issues of post-Brexit convergence with EU regulations needed to be negotiated one by one.
"I am up for co-operation, I believe co-operation between our two states is good and in many areas is vital."
He added: "There are other areas where, frankly, divergence will come about on those regulations because we in Northern Ireland, being part of the UK, believe we are going in a different direction."
Adhering to certain EU policies would hold Northern Ireland back, the North Antrim MP added.
That included areas like agriculture.
"We are not about convergence here, we are about co-operation."
Yesterday, Mr Paisley was criticised for calling on the British government to make life hard for the Republic over Brexit and "shake their cage".
The MP said the UK could make a fisheries deal "extremely long, tedious and hard for them", claiming Dublin had acted "disgracefully".
The Department for Exiting the EU (DExEU) refused to comment on a report in The Times 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.
A well placed figure told The Times that the DUP, on whose votes the Prime Minister relies on in the Commons, would be prepared to give the green light to a deal that offered to maintain regulatory alignment in agriculture and energy after Brexit
In return EU leaders are prepared to offer a two-year Brexit transition deal as early as January.
However, Irish agriculture minister Michael Creed told BBC2's Newsnight that 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."
The border issue has emerged as a major sticking point in the Brexit talks in the run-up to a crunch EU summit on December 14 and 15.
Theresa May is desperately hoping EU leaders will give the green light for the second phase of the negotiations - including talks on a free trade deal - to begin.
