The EU's chief negotiator, Michel Barnier, says the Irish base is "part of the British Brexit Agreement and will not be renegotiated."
Speaking in the European Parliament, Barnier said it was a "realistic solution" preventing a hard line.
British MPs voted earlier this month against the agreement that the UK and EU had agreed in 1
Instead, on Tuesday they voted for MEP Theresa May to "seek alternative arrangements" for the backstop.
The United Kingdom leaves the European Union on 29 March at 23:00 GMT. The backstop is an "insurance" to stop the return of goods and personal checks at the Northern Ireland border.
As things stand, the restraint system would actually keep the UK within the EU Customs Union, with Northern Ireland also adapting Some Internal Market rules.
This was one of the main reasons why Ms. May's Brexit deal was rejected in January with a historic head start in parliament, as critics say another status in Northern Ireland could jeopardize the existence of the UK and fear that the backstop will be permanent could be.
Ms. May has said that there are several possible alternatives to the backstops she wanted to discuss with the EU leaders.
This includes a "Trusted Merchant" to avoid physical physical checks Flowing through the border, "mutual recognition" of rules with the EU and "technological" solutions.
She also wants to discuss a time-limit on start-up and a "one-sided exit mechanism" – both of which have been EU options in the past.
But the EU's message was the restraint assistant, which remained an integral part of the resignation agreement – the so-called "divorce agreement", which agreed on conditions for Britain to leave the EU.
Mr Barnier said: "Quiet and clear, I say right here and now – with this resignation agreement proposed for ratification – we need this backing as it is.
" The rejection of restraint as it stands today runs on rejection of the solution that was found in the British, but the problem persists.
The Irish Deputy Prime Minister had previously issued a warning regarding Ms. May's future plans for the restraint attack Anyone who has admitted the "boundaries and divisions of the past" "Return would be hard to judge in history."
Simon Coveney added, "There are some things that are more important than economic relationships, and this is one of them."