DUP leader Sir Jeffrey Donaldson has described the “wall being broken” on the Northern Ireland Protocol.
Mr Donaldson made the claim after the EU had earlier confirmed plans to bring new proposals to deal with the protocol.
Speaking to BBC’s Talkback programme, Mr Donaldson said he didn’t expect the new proposals to be acceptable but said it would prompt further negotiation.
Mr Donaldson said the change of tone from the EU was as a result of “unionists standing together”.
“We were told weeks ago the EU were not in a position they were ever going to reopen negotiations. I think we have breached the first wall,” said Sir Jeffrey.
"I think the pressure we have brought to bear...has focused minds both in London and in Brussels.
"We still have a long way to go, I don’t pretend otherwise. We have opened up the protocol there is the beginning of a negotiation, we will see what emerges from that.
“The EU can call it what they will, they can present it whatever way they wish, but in the end the wall has been breached.”
Ulster Unionist finance spokesperson Steve Aiken said the Government must insist “at a bare minimum” on the introduction of easements detailed in the UK Command Paper.
He added: “We await with interest the EU proposals to deal with the real challenges that the Protocol is imposing on all of the people of Northern Ireland.
“However, Mr Sefcovic’s statement today that he ‘welcomed’ the ongoing and increasing trade diversion between NI and the Irish Republic and his lack of recognition that the Protocol has significantly undermined the Belfast Agreement, shows he is guilty of selective listening despite his recent trip to Northern Ireland.”
The proposals are expected to be issued by the "middle of next week", Marcos Sefcovic has said.
The European Commission Vice President said he hopes the proposals will be considered in new talks with the UK.
The EU official made the comments in Dublin on Thursday.
The renewed talks to solve the protracted issue are expected to begin before the end of October, with talks to continue throughout November with a view to concluding before the end of the year.
The proposals will focus on animal checks (SPS), customs, medicine supplies and providing a voice for Northern Irish representatives in the EU.
Mr Sefcovic said the new proposals would be "very far reaching" and that he hoped they would be seen as such.
He added: "I think it is the best interest of both of us that we will try to find a reasonable solution before the end of the year, early next year.
"It's a very simple proposal but from our perspective these would be really, I would say, very far-reaching proposals.
"I sincerely hope that it will be seen as such by our UK counterparts and they engage constructively in our discussion, because I think we have to move from the tough political rhetoric, from the threats we hear all the time, down to the business that actually solves the problems."
The intervention comes after Brexit Minister Lord Frost told the Conservative Party conference earlier in the week that the UK could trigger the Article 16 safeguard mechanism as part of the NI Protocol.
Lord Frost said action could be taken by Christmas as he called for “short, intensive” talks with the EU to get under way swiftly.
He told the conference in Manchester that he would “soon be sending” new legal texts to the EU with proposals to resolve the “serious political problem”.
“I hope that might change over the next couple of weeks or so. It does need to be resolved though, one way or another, whether it’s through negotiations or Article 16,” he told a fringe event arranged by the Policy Exchange think tank.
On Wednesday, Irish Foreign Affairs Minister Simon Coveney said that he did not think it was likely that Boris Johnson’s Government would take what is seen to be the nuclear option of triggering Article 16.