Britain on Thursday told the EU that it would have no choice but act “if the EU would not show the requisite flexibility to help solve” problems caused by the Northern Ireland Protocol.

The remarks came during a phone call between British Foreign Secretary Liz Truss and EU’s Vice President Maros Sefcovic, according to a government statement.

Truss told Maros 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 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.”

Underlining the importance of defending the 1998 Belfast (Good Friday) Agreement, Truss said the European Commission “bore a responsibility to show more pragmatism and ensure the Protocol delivered on its original objectives.”

She also reiterated British proposals to “fix the Protocol” during the call and stressed, “why EU proposals would take us backwards, by creating more checks and paperwork.”

However, Sefcovic said that “there was no room to expand the EU negotiating mandate or introduce new proposals to reduce the overall level of trade friction,” reiterating the EU’s ongoing stance on the issue.

“The Foreign Secretary noted this with regret and said the situation in Northern Ireland is a matter of internal peace and security for the United Kingdom, and if the EU would not show the requisite flexibility to help solve those issues, then as a responsible government we would have no choice but to act,” the statement added.

The Northern Ireland Protocol necessitates border checks on any animal and plant-based products, including frozen meat and processed meat products before their transport to Northern Ireland, which is aligned with EU rules and regulations.

The protocol creates a de facto trade border in the Irish Sea between Northern Ireland and the rest of the UK.

The UK left the bloc on Jan. 31, 2020, as a result of a 2016 referendum that ended the country’s more than 40-year-long membership in the European club.

The agreement signed by the sides included the Northern Ireland Protocol, which practically avoided a hard border between Northern Ireland and the Republic of Ireland.

The Democratic Unionist Party (DUP), which lost last week the position of being the biggest party in Northern Ireland after the historic Sinn Fein win in the assembly election, has said it would not take part in a new Executive unless the protocol is sorted.

The DUP had supported the first Boris Johnson government, which hammered the EU Withdrawal Agreement and the additional protocol on Northern Ireland.

The unionist party, however, has said the protocol is keeping Northern Ireland apart from the rest of the UK, an idea which has also been voiced by the central UK government since Brexit.