The European Union is launching legal action against the U.K. in response to unilateral moves to rewrite parts of the Northern Ireland Protocol in the post-Brexit deal between both sides, the bloc’s executive branch said Wednesday.
The proposed U.K. bill seeks to remove customs checks on some goods entering Northern Ireland from the rest of the U.K. That will override parts of the trade treaty that Prime Minister Boris Johnson signed with the E.U. less than two years ago.
The E.U. believes that the UK’s unilateral decision is violating international law. The so-called Northern Ireland Protocol is the part of the Brexit deal that keeps Northern Ireland in the E.U.’s single market for goods.
The 27-nation bloc will restart the infringement procedure launched against the U.K. government last year after Britain unilaterally extended a grace period that applies to trade on the island of Ireland.
Read more: Brexit Is Still a Hot Mess
The action had been put on hold in September 2021 as both parties tried to find joint solution. In addition, the E.U. will kick off further action against the U.K. for a perceived failure to carry out necessary controls under the E.U. rules, and to provide trade statistics data as required under the protocol.
In the final stages of an infringement procedure, which can last for months, the European Commission can refer such cases to the bloc’s highest court. The European Court of Justice has jurisdiction to rule on matters of E.U. law in Northern Ireland.
Northern Ireland is the only part of the U.K. that shares a border with an E.U. country—the Republic of Ireland. When Britain left the E.U. and its borderless free-trade zone, the two sides agreed to keep the Irish land border free of customs posts and other checks because an open border is a key pillar of the peace process that ended decades of violence in Northern Ireland.
Instead, to protect the E.U.’s single market, there are checks on some goods, such as meat and eggs, entering Northern Ireland from the rest of the U.K.
British unionists in Northern Ireland say the new checks have put a burden on businesses and frayed the bonds between Northern Ireland and the rest of the U.K.—seen by some unionists as a threat to their British identity.
Read more: Irish Unity: Could Reunification Happen?
Britain’s Conservative government says the Brexit rules also are undermining peace in Northern Ireland, where they have caused a political crisis. Northern Ireland’s main unionist party is blocking the formation of a new power-sharing government in Belfast, saying it won’t take part until the Brexit trade rules are scrapped.
More Must-Read Stories From TIME