EU initiates legal action against U.K. over plans to break Brexit treaty

The European Union's chief executive on Thursday initiated legal proceedings against the U.K. over Prime Minister Boris Johnson's plans to break international law to override parts of the Brexit deal the two sides struck last year.

Why it matters: It's a sign of a major breakdown in the U.K.-EU relationship and deals a blow to the odds of the two sides successfully negotiating a free trade agreement before the Brexit transition period expires at the end of the year. Investors and trade experts fear a "no-deal" Brexit on Dec. 31 could cause massive economic disruptions.

The state of play: The letter of "formal notice" gives Johnson a month to make changes to his proposed internal market bill, which the U.K. government admitted breaks international law "in a very specific and limited way," before the matter reaches European courts.

• The bill as it stands would allow U.K. ministers to unilaterally determine which goods should be subject to EU checks and tariffs when passing from Great Britain to Northern Ireland, which shares a land border with the Republic of Ireland (an EU member).
• The House of Commons passed the bill this week in spite of a small rebellion by members of Johnson's party and condemnation by all five living former U.K. prime ministers. It now faces resistance in the upper House of Lords.

Go deeper: Brexit threatens to become a constitutional crisis