The foreign secretary told European Commission vice-president Maros Sefcovic that the bloc needed to budge during a “tetchy” phone call this morning.
She said a failure to do so would leave the UK with “no choice” but to tear up the agreement on trade between Great Britain and Northern Ireland.
But in response, Sefcovic said the EU had moved as far as it could and would be making no further concessions.
He said: “The EU cannot solve all the problems created by Brexit and the type of Brexit that the UK chose.
“That is the reason why the EU’s position has been consistent: we will not renegotiate the protocol, and the EU is united in this position.
“Unilateral action, effectively disapplying the protocol, is not a solution for the way forward.”
He said the commission “stands ready” to carry on working for a joint solution to the frictions being caused by the accord, and urged the UK “to do the same”.
The UK insists the Protocol, which created a customs border in the Irish Sea, must be radically redrawn in order to protect the Good Friday Agreement and restore power-sharing government at Stormont.
If no agreement is reached, legislation over-riding parts of the Protocol is set to be introduced by ministers next week – a move which could trigger a trade war between the UK and EU.
In a statement issued after the call between Truss and Sefcovic, a Foreign Office spokesperson said: “The Foreign Secretary outlined that the UK’s overriding priority is to protect peace and stability in Northern Ireland and said that the Northern Ireland Protocol had become the greatest obstacle to forming a Northern Ireland Executive.
“She also noted that the current situation was causing unacceptable disruption to trade and had created a two-tier system where people in Northern Ireland weren’t being treated the same as everyone else in the UK.
“She reminded Vice President Šefčovič of the importance of defending the Belfast [Good Friday] Agreement, and said that the commission bore a responsibility to show more pragmatism and ensure the protocol delivered on its original objectives.”