Liz Truss has claimed the east-west relationship between Great Britain and Northern Ireland has been “undermined” by the Northern Ireland protocol, as she confirmed plans to table legislation that would scrap parts of the agreement. The UK foreign secretary, who is also responsible for Brexit, set out plans for the move in a statement in the House of Commons. The bill is not expected to be published for several weeks, but if enacted could spark a trade war with the EU. Truss said the government’s first priority was to uphold the Good Friday agreement, which she said was “under strain”. “The Northern Ireland protocol does not have the support necessary in one part of the community in Northern Ireland,” she said, referring to opposition from the Democratic Unionist party. Citing issues such as the need for veterinary checks and EU rules that prevented the Treasury from cutting taxes, she said: “These practical problems have contributed to the sense that the east-west relationship has been undermined,” adding: “We need to restore the balance in the agreement.” As expected, she proposed legislation that would create a “green channel” for goods going to Northern Ireland from Great Britain that would not go on to the Republic of Ireland, with mandatory checks halted for these exports. Goods moving onwards to the Republic would still face checks, via a “red channel”. This new system would involve a trusted trader scheme using real-time commercial data. Truss said the changes would create a “dual regulatory system, that encompasses either EU or UK regulation as those businesses choose; that reflects its unique status of having a close relationship with the EU, while being part of the UK single market”. The legislation would also remove regulatory barriers to goods made in Great Britain being sold in Northern Ireland and allow the UK to determine tax and spending. The European Commission’s vice-president in charge of Brexit, Maroš Šefčovič, said Truss’s proposals raised “significant concerns”, adding that “unilateral actions contradicting an international agreement are not acceptable”. In a statement after Truss’s speech to the Commons, Šefčovič said: “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.” EU diplomats say no decision has been taken on the nature of retaliatory action, which would only follow a move by the UK government to override the protocol. EU officials have been urging the UK to return to the negotiating table to discuss proposals from Šefčovič that they say would sharply reduce checks on goods moving between Great Britain and Northern Ireland. “With political will and commitment, practical issues arising from the implementation of the protocol in Northern Ireland can be resolved,” Šefčovič said. Boris Johnson insisted the government was not seeking to overturn the protocol, telling the BBC, “we don’t want to nix it, we want to fix it”. He insisted the move would not breach international law, saying: “The higher duty of the UK government in international law is to the Good Friday agreement and the peace process. “That’s the thing we have to really look to, and of necessity we can make some changes I think to the protocol, which is not the law of the Medes and the Persians [a Biblical reference, denoting something unchangeable].” The DUP’s Westminster leader, Jeffrey Donaldson, said Truss’s statement was: “a welcome, if overdue step, that is a significant move towards addressing the problems created by the protocol, and getting power-sharing, based upon a cross-community consensus, up and running again”. His party would like to see progress on the legislation “in days and weeks, not months”, he said. Truss stressed that she was still committed to negotiations with the EU, and was hopeful an agreement could be reached. Boris Johnson on Monday described the legislation as “insurance” in case the talks did not yield changes to the operation of the protocol. Earlier, the prime minister’s official spokesperson said the legislation was aimed at resolving “serious and grave” problems with the protocol – not scrapping it altogether, and added that there would be “robust penalties” for businesses failing to comply with the rules. Government sources were adamant the legislation would not breach international law, although they declined to discuss the details of legal advice provided to ministers by the attorney general, Suella Braverman.