Brussels has warned the British Prime Minister that his attempt could scupper any chance of a trade deal.
After Britain explicitly asserted its intentions to act outside international law by breaching the Brexit divorce treaty, EU negotiators are trying to gauge how to deal with London.
Britain signed the treaty and formally exited the EU in January, but remains within the single market until the end of this year under a status quo agreement.
European Commission Vice President Maros Sefcovic will travel to London to meet British counterpart Michael Gove for the emergency talks alongside scheduled trade talks between chief negotiators Michel Barnier and David Frost.
"The EU seeks clarifications from the UK on the full and timely implementation of the Withdrawal Agreement," a European Commission spokesman said.
After the hectic twists and turns of the Brexit crisis, Europe's leaders have been handed an ultimatum by Britain: accept the breach of the treaty or prepare for a messy divorce when Britain finally disentangles at the end of the year.
Talks on a new trade deal have so far snagged on state aid rules and fishing.
Without an agreement nearly $1 trillion in trade between the EU and Britain could be thrown into chaos at the beginning of the year, an economic hit neither side needs as they try to limit the damage from the coronavirus crisis.