European Commission president Ursula von der Leyen warned Britain on Wednesday that proposed legislation that rolls back terms of the Brexit deal would break international law if passed.

"Very concerned about announcements from the British government on its intentions to breach the withdrawal agreement. This would break international law and undermines trust," von der Leyen tweeted.

In Latin, a language often used by British Prime Minister Boris Johnson, the former German defence minister insisted that "pacta sunt servanda " or "agreements must be kept" and that this was foundation of good relations. 

Johnson's government shocked Brussels on Monday with its surprise announcement that it would submit a bill that intentionally breaches its EU divorce treaty, though it said for only technical reasons.

London maintains the changes would smooth post-Brexit trade within the United Kingdom and help power a recovery from the coronavirus pandemic.

Maros Sefcovic, the EU vice president in charge of overseeing implementation of the divorce deal, said he had demanded an emergency meeting with Britain to discuss the law.

"I made it clear that the withdrawal agreement is not open for renegotiation," Sefcovic told reporters after a call with his UK counterpart Michael Gove, a senior minister.

"We expect the letter and spirit of the withdrawal agreement to be fully respected," he added.