Emergency talks as the divorce gets messier.
European Union chief negotiator Michel Barnier arrived in London just after the UK revealed plans to undercut parts of the Brexit divorce treaty.
London is set to unveil legislation for life outside the EU - and the government has admitted it will break international law.
Brussels has warned that could scupper any chance of a trade deal.
Now Thursday's (September 10) emergency talks will take place alongside Barnier's regular trade negotiations.
Sources have told Reuters the EU might even take legal action over the UK legislation.
After Britain explicitly stated that it would act outside the law, negotiators are trying to gauge how to proceed.
Europe's leaders have effectively been handed an ultimatum: accept the breach of the treaty or prepare for a difficult divorce at the end of the year.
Britain formally left the EU on January 31st.
But talks on a new trade deal before the end of a status-quo transition arrangement in December have snagged, particularly on state aid rules and fishing.
Without a deal $1 trillion in trade between the EU and Britain could be thrown into chaos.
Now the UK legislation could just be a negotiating gambit.
European diplomats say Britain is playing a game of Brexit chicken, and challenging Brussels to blink first.
Some, though, fear Johnson may view a no-deal exit as a useful distraction from the coronavirus crisis.