LONDON — Boris Johnson’s government on Monday introduced legislation that threatens to rip out a central plank of the very Brexit deal the prime minister hailed as a victory — the agreement with the European Union that controls how goods move between Britain and Northern Ireland. The highly controversial bill, coming just a week after Johnson survived a no-confidence vote, prompted pushback from European diplomats, the Irish prime minister and members of Johnson’s own party, charging that the unilateral turnaround would violate international law and could spark a trade war with the continent. The British government is also wary of backlash from the White House and Congress. U.S. politicians, including President Biden, have repeatedly warned Johnson not do anything that might undermine the peace in Northern Ireland. House Speaker Nancy Pelosi has threatened that there will never be a trade deal with the United States if the prime minister upsets the status quo. Johnson claimed Monday that he is in fact trying to preserve the peace by walking away from what’s known as the “Northern Ireland Protocol” — which he negotiated, concluded and cheered in 2020. Johnson’s critics say he either never read his own deal, or never understood it, or simply hoped to fudge the details later. Fudging has been a central theme during his tenure. The House of Commons is investigating whether he lied about boozy parties staged at his offices and residence at Downing Street during coronavirus pandemic lockdowns. U.K. to investigate whether Boris Johnson lied about lockdown parties Johnson originally praised the Brexit trade protocol as an artful compromise — allowing Britain to break free while also retaining the integrity of the E.U. market and maintaining the free flow that has helped to cement peace on the island of Ireland. He dismissed concerns from Northern Ireland’s unionists that the agreement would lead to a customs-and-control regime for goods moving across the Irish Sea. But now, he says it’s critical to acknowledge that unionists feel cut off from the rest of Britain. He told broadcasters Monday: “We have to understand there are two traditions in Northern Ireland, probably two ways of looking at the border issues, and one community at the moment feels very, very estranged from the way things are operating and very alienated. And we’ve just got to fix that.” The new bill would remove blanket checks on goods moving between Britain and Northern Ireland, instead creating “green lanes” with little paperwork and “red lanes” with more scrutiny. It also demands that trade disputes be resolved by “independent arbitration” and not the European Court of Justice. On Monday, Irish Prime Minister Micheál Martin told reporters, “It’s very regrettable for a country like the U.K. to renege on an international treaty.” Martin continued, “I think it represents a new low point, because the natural expectation of democratic countries like ourselves, the U.K. and all across Europe is that we honor international agreements that we enter into.” British Foreign Secretary Liz Truss said she has tried hard to find compromise with the Europeans. Ireland’s minister for foreign affairs, Simon Coveney, accused the British government of proposing to “deliberately ratchet up tension with an E.U. seeking compromise.” He said Truss hadn’t met with her counterparts since February. On one level, this is all about trade minutiae and paperwork — how a chicken or an egg, or pharmaceuticals and car parts, need to be inspected and taxed as the goods cross the Irish Sea, and how any of those goods move into Europe’s Common Market through an Irish back door. On a deeper level, this is all about the future of the United Kingdom, and whether Northern Ireland remains a part of that kingdom, or slips away, as Scotland threatens to do, creating a shrinking British state, under Johnson or his successors. At stake: The Good Friday Agreement, the 1998 truce that brought peace to Ireland, ending the 30-year sectarian civil strife known as “the Troubles.” The pact, negotiated in part by the United States, erased the militarized border between Northern Ireland and the Republic of Ireland and created a balky, dysfunctional but peaceful sharing of power in Belfast between unionists and republicans, pro-Britain Protestants and pro-Ireland Catholics. Unionists in Belfast are now refusing to participate in power sharing institutions until the trade situation is addressed. But on Monday, 52 out of 90 members of the Northern Ireland Assembly signed a letter rejecting “in the strongest possible terms” Johnson’s attempt to rewrite the protocol. The assembly members called his move “reckless.” At Westminster, too, some lawmakers from Johnson’s Conservative Party worried that it could reopen the Brexit debate and treaties. Critics say Johnson is yielding to extremist elements threatening violence. For his part, Johnson on Monday called the proposed changes his government seeks a “trivial adjustment.” Truss said the new bill will “fix the problems with the Northern Ireland Protocol and restore political stability.” She said she hoped that the Brussels would be “willing to change.” Maros Sefcovic, a European Commission vice president, said that the U.K.’s move to unilaterally override the Northern Ireland Protocol was “damaging to mutual trust and a formula for uncertainty.” David Henig, a trade policy expert, said that the unresolved Northern Ireland issue may already be having a “chilling effect” on where companies invest and locate. Henig said that while the Biden administration has made its stance clear, “it really could do with being a little bit more hands on.” For instance, “there still isn’t an envoy to Northern Ireland, and there are no sign of U.S. suggesting mediators or that they could facilitate dialogue.” Karla Adam contributed to this report.