The EU has announced new legal action against the UK government over its plans to scrap parts of the post-Brexit deal for Northern Ireland.
Ministers outlined a bill on Monday aimed at unilaterally changing trade, tax and governance arrangements in the 2019 deal.
The treaty was agreed by both sides but the UK says it has disrupted trade and power-sharing in Northern Ireland.
But the EU says overriding parts of the deal would break international law.
European Commission vice-president Maros Sefcovic said there was "no legal or political justification whatsoever for unilaterally changing an international agreement".
"So let's call a spade a spade, this is illegal," Mr Sefcovic said, adding that the UK's decision "left us with no choice" but to take legal action.
Prime Minister Boris Johnson's spokesperson said his government was disappointed the EU had taken legal action and continued to favour a negotiated resolution.
The Northern Ireland Protocol is a special arrangement that keeps Northern Ireland in the EU's single market for goods, avoiding a hard border with the Republic of Ireland.
The arrangement ensured free trade could continue across the Irish land border, which is a sensitive issue because of the history of conflict in Northern Ireland.
But the protocol brought in some new checks on goods moving between Great Britain and Northern Ireland and has been criticised by unionist politicians.
However, the majority of politicians elected to the Northern Ireland Assembly in last month's elections support the arrangements.
The European Commission said it would restart legal action - paused in March 2021 - over the UK's decision to delay checks on certain goods arriving into Northern Ireland from Great Britain.
The Commission also launched two new proceedings over claims the UK has failed in its obligations to share trade data and set up border inspection posts.
These legal steps could eventually lead to the UK being fined under a dispute process overseen by the European Court of Justice (ECJ).
But the dispute process can take months to complete and the Commission has insisted its "door remains open" for talks with the UK to find a resolution.
