BRUSSELS (Reuters) - The European Commission opposes extending British membership of the European Union to June 30 as British Prime Minister Theresa May proposed on Wednesday, according to an EU document seen by Reuters.

In a note on the Brexit process reviewed by the Commission at its weekly meeting on Wednesday, officials wrote that leaders meeting May at a summit on Thursday faced a “binary” choice of a short delay of Brexit from March 29 to before May 23 or a long delay to at least the end of this year, with Britain obliged to hold an election on May 23 for European Parliament lawmakers.

“Any extension offered to the United Kingdom should either last until 23 May 2019 or should be significantly longer and require European elections,” the document said. “This is the only way of protecting the functioning of the EU institutions and their ability to take decisions.”

EU states which were due to receive additional legislative seats after Brexit would need to know by mid- to late April if they would be denied those seats because Britain was staying.

The note also said that in any extended membership, Britain should, “in a spirit of loyal cooperation”, commit to “constructive abstention” on key issues, such as the EU’s long-term budget and filling top EU posts after the May election.