The EU has “significant concerns” about the UK’s intention to introduce legislation to change the Northern Ireland protocol, says vice-president of the European Commission Maroš Šefcovic in a statement.
The EU also warned of potential EU action in response to Ms Truss’ announcement earlier on Tuesday.
“Should the UK decide to move ahead with a bill disapplying constitutive elements of the protocol as announced today by the UK government, the EU will need to respond with all measures at its disposal,” the statement read.
It raises the prospect of renewed legal action by the EU against Britain, and ultimately a potential trade war between the two sides with tariffs placed on goods.
“With political will and commitment, practical issues arising from the implementation of the protocol in Northern Ireland can be resolved,” the statement read, adding that the Commission “stands ready to continue playing its part”.
EU proposals already set out have the potential to resolve the issues raised about the protocol, it continued.
“The EU has shown understanding for the practical difficulties of implementing the protocol, demonstrating that solutions can be found within its framework,” the statement read, adding that “additional far-reaching and impactful bespoke arrangements” have been put forward to allow the flow of goods across the Irish Sea.
“The European Commission stands ready to continue discussions with the UK government.”
The Minister for Foreign Affairs Simon Coveney reacted by saying that the actions of the British government “contrary to the wishes of people and business in Northern Ireland”.
“I deeply regret the decision of the British government to introduce legislation in the coming weeks that will unilaterally disapply elements of the protocol on Ireland/Northern Ireland,” Mr Coveney said in a statement.
“Such unilateral action in respect of an internationally binding agreement is damaging to trust and will serve only to make it more challenging to find solutions to the genuine concerns that people in Northern Ireland have about how the protocol is being implemented.”
He said that the British move “undermines political stability and confidence in Northern Ireland’s economy.”
Business group CBI Northern Ireland said the last thing companies wanted was further uncertainty in trading arrangements at a time when the most vulnerable in society are dealing with the worst cost of living crisis in decades and firms are “reeling” from the rising cost of doing business.
“Now more than ever, flexibility and compromise are needed from both sides to reach lasting trade solutions, securing peace and prosperity,”said the group’s director Angela McGowan.
“With good political will, a landing zone can undoubtedly be found so that GB-NI trade flows are smoothed.”
Earlier, EU commissioner Mairead McGuinness said there has been “a lot of spinning” by the UK in the past week around the Northern Ireland protocol.
Ms McGuinness acknowledged that relations between the UK and the EU were strained, but said the EU had the political will to resolve the outstanding issue of the protocol. “We have to do it together,” she said.
She said any threat of unilateral action by the UK would not do anything to unlock the problems for the people of Northern Ireland who do not want further destabilisation.
Speaking on RTÉ’s Morning Ireland Ms McGuinness said, there will not be a knee-jerk reaction from the EU, which has “tried to remain very calm”.
“We put forward a lot of proposals, but there hasn’t been a lot of engagement,” she said. “The truth is Northern Ireland was not considered during the [Brexit] referendum in 2016.”
The idea that the UK could “tear up” what was on the table and “start from scratch” was a delaying tactic, Ms McGuinness said, adding that the issue could be solved with political will, but unilateral action would make the situation worse.
Her comments followed UK prime minister Boris Johnson's visit to Northern Ireland on Monday. Mr Johnson signalled that his government would begin the process of taking unilateral action to remove parts of the Northern Ireland protocol – while insisting the post-Brexit deal would not be scrapped but "fixed".
Mr Johnson travelled to the North to meet the five main political parties in a bid to restore Stormont power-sharing, which effectively collapsed last Friday after the Democratic Unionist Party (DUP) blocked the election of a Speaker as part of its continuing protest over the protocol.
Following talks in Hillsborough Castle, Mr Johnson said he tried to persuade the DUP “in particular” to return to governing.
The protocol is part of the EU-UK Brexit deal that allows goods to pass freely between Northern Ireland in the UK and the Republic of Ireland in the EU. The UK voted to leave the EU in 2016, requiring a deal on the post-Brexit trading rules applying to Northern Ireland to allow this to happen.
It was designed to prevent a hard border on the island of Ireland but unionists argue the solution (a new Irish Sea trade border) undermines Northern Ireland’s place in the United Kingdom
In the business world, companies and other traders say this has added significantly to their administrative burden and that this burden will only increase with the expiry of grace periods introduced by the UK to delay the full checks.