The European Commission’s vice president will meet with Michael Gove later over the Northern Ireland Protocol.
Maros Sefcovic is travelling to London for the meeting after making it clear the bloc regards the protocol as the only way forward.
He expressed concerns over “teething problems” in the implementation of the protocol but said it was now “our mutually agreed legal obligation”.
It comes amid tensions after the brief triggering by the bloc of Article 16, with particular ire among unionists in Northern Ireland who are calling for it to be ditched.
The protocol was designed to prevent a hard border with Ireland but has resulted in additional checks for goods crossing from Great Britain to Northern Ireland.
A UK government spokesperson said it was “disappointing that the Commission has failed to acknowledge the shock and anger felt right across the community in Northern Ireland from its decision to trigger Article 16, and the need to take urgent steps to restore confidence as a result”.
They added: “The Chancellor of the Duchy of Lancaster will underline the need for such action and political leadership in this regard when meeting with Vice-President Sefcovic in London.”
The region’s First Minister Arlene Foster has urged Mr Gove and Boris Johnson “act on” their unionist beliefs.
Mrs Foster accused the EU of not respecting the sovereign territory of the UK.
The DUP leader said the issues with the protocol are “fundamental”, adding: “You can’t even get a pot plant from Great Britain into Northern Ireland at the moment which is absolutely incredible.”
UUP leader Steve Aiken said the letter “reeks of arrogance and intransigence”.
“Instead of protecting the Belfast Agreement and defusing tensions, this letter will do the exact opposite,” he said.
He also claimed that Northern Ireland is being used as a “punchbag in the EU`s confrontations with the UK Government”.
On Wednesday European Commission president Ursula von der Leyen apologised for “mistakes” that led to the triggering of Article 16.
However Mr Sefcovic has made it clear in his letter that the commission regards the protocol as the only way forward.
“The protocol is the solution agreed by the UK and the EU to these challenges: it is the only way to protect the Good Friday (Belfast) Agreement, preserving peace and stability and avoiding a hard border on the island of Ireland,” he wrote.
“It is designed to ensure clarity and predictability for people and businesses, while minimising the disruption inevitably caused by the withdrawal of the United Kingdom from the European Union.
“It is a balanced outcome after years of difficult negotiations and is now our mutually agreed legal obligation.
“I therefore agree that our shared objective is to work tirelessly in order to make the protocol work.
“It requires full and faithful implementation by both parties.”