Jean-Claude Juncker, the president of the European Commission, says Britain should leave the EU by the start of elections to the European Parliament on May 23 if the country is not taking part, AP reported.

That’s earlier than the request British Prime Minister Theresa May has made. In a letter to the EU, May wants EU leaders to back an extension to the Brexit date from March 29 to June 30.

An EU Commission official said Juncker told May in a telephone call that “the withdrawal has to be complete before May 23,” the first day of the European elections.

The official, who asked not to be identified because of the sensitivity of the situation, said that if the deadline comes later Juncker warned May that “we face institutional difficulties and legal uncertainty.”

He insisted EU elections would have to be held in Britain if a June 30 date was asked for.

The 27 EU nations meeting in a summit Thursday need to back an extension to the deadline unanimously.