The procedure against the U.K. could also serve the Commission as a necessary legal preparation to potentially proceed with the inauguration of the new Commission by December 1 | Matt Cardy/Getty Images Brussels launches legal action against UK over failure to nominate commissioner The UK government argues it cannot make a significant international appointment in a run up to an election.

The European Commission launched an infringement procedure against the U.K. on Thursday over its refusal to nominate a candidate for EU commissioner.

"As the Guardian of the Treaties, the European Commission has today sent a letter of formal notice to the United Kingdom for breaching its EU Treaty obligations by not suggesting a candidate for the post of EU Commissioner," a Commission press release said. "The U.K. authorities have until Friday 22 November at the latest to provide their views [on the launched procedure]. This short time period is justified by the fact that the next Commission must enter into office as soon as possible."

Commission President-elect Ursula von der Leyen and her team hope to take office on December 1 — a month behind schedule — but the U.K. has so far refused, despite two written requests by von der Leyen, to put forward a nominee for commissioner.

Britain’s Ambassador to the EU Tim Barrow wrote to the Commission on Wednesday night saying that Britain won't nominate a candidate before the general election on December 12, despite having agreed to do so as part of a deal that postponed the Brexit deadline to January 31. Neither side has made the contents of the letter public.

"We have written to the EU to confirm that pre-election guidance states the U.K. should not normally make nominations for international appointments during this period," said spokesperson for the U.K. government.

"The Commission ... considers that the U.K. is in breach of its EU Treaty obligations," said the press statement, while rejecting the British argument that London cannot nominate a commissioner because of the period of election "purdah."

"The European Commission recalls that, in accordance with established EU case-law, a Member State may not invoke provisions prevailing in its domestic legal system to justify failure to observe obligations arising under Union law," it said.

The procedure against the U.K. could also serve the Commission as a necessary legal preparation to potentially proceed with the inauguration of the new Commission by December 1, even if the U.K. still has not nominated a Commissioner by then, an EU diplomat said.