The apparent irony of the move was slammed as "bizarre and unacceptable".
MEPs have controversially held a secret ballot... on their own transparency.
The concealed vote was held on reforms to rules governing which lobbyists European politicians can hold meetings with.
Votes are normally recorded in the European Parliament.
Centre-right MEPs from the European People’s Party decided to ask for the secret ballot at a meeting earlier this month.
Their move was criticised by campaigners as “bizarre and unacceptable”.
The secret ballot was held on Thursday (January 31) on two changes to the European Parliament’s rules of procedure.
They involved obliging MEPs to only meet lobbyists that have put themselves on the EU’s transparency register and to publish details of them online.
Both elements were approved, sources told Euronews.
Brussels is said to have 15,000 lobbying organisations, who attempt to influence how EU legislation evolves.
Their interaction with MEPs and European Commission officials is a long-running controversy in the EU capital.