Jean-Claude Juncker and the German 'moonlighting' claims
Friends of Jean Claude-Juncker, the man odds-on to become the next president of the European Commission, have defended him against attacks that he is not open enough about his fee-earning work for business groups.
German newspapers have raised questions about whether it is proper for him to be taking money for meeting influential groups without giving full details.
An editorial in Bild under the headline "All cards on the table" is scathing: "He wants to say only the bare essentials about his well-remunerated speeches. That might work in his home country of Luxembourg, which is famous for its banking secrecy, but not in Brussels."
But friends have told the BBC that Mr Juncker is not obliged to make public how much money he has earned for addressing executives. Recently, he met business leaders from the German arms industry and the tyre industry. His critics said he should disclose what fees were charged for addressing those meetings.
There is no suggestion of impropriety or illegality, only that more openness would be desirable. Transparency International told the BBC that candidates for jobs like president of the European Commission "should declare outside sources of income".
If he does get the job, he will have to make a declaration. But the question was over his work for particular industries while he was a candidate.
"We need to be very clear about outside interests," said Carl Dolan, who speaks for Transparency International from its Brussels office which monitors the EU.
The controversy arises because Mr Juncker is on the books of at least two international agencies which provide speakers for private events. The fees involved are not published - though an estimate of 15,000 euros (£12,000; $20,400) as the going rate per speech has not been challenged.
He has given four speeches in all. German newspapers are now referring to the matter as the "Moonlighting Job Affair".
Bild is important in this context because it is not just a reporter of events but an influential "maker of the weather" when it comes to the selection of the next president of the European Commission.
A month ago, it seems to have influenced Chancellor Angela Merkel and prompted a change of position. She switched from a lack of strong support for Mr Juncker to firm endorsement after the paper published a strident editorial against jettisoning him.
It is now saying that Mr Juncker should set a "shining example when it comes to transparency".
Those who want more openness about the finances and interests of politicians say that when they agree to speak to businesses for money, they might offer the perception that doors have been opened for them in future.
Law has been tightened with regard to the members of the European Parliament but not for candidates to the top posts in the bureaucracy. Transparency International would like much tougher "integrity checks" for candidates.
When contacted by the BBC, Mr Juncker's office would not comment. His defenders say that he has made a declaration of interests to the Luxembourg parliament of which he is a member, and that he currently does not have a job with the EU.
Mr Juncker is listed as a speaker by at least two agencies. Premium Speakers International organises engagements for him. It describes him as a "consummate European" and "one of the founding fathers of the euro".
Making similar points, the London Speaker Bureau notes he was awarded the International Charlemagne Prize of Aachen for his contribution as an "engine and pioneer of European unification".
The glowing endorsement is unlikely to be viewed with enthusiasm by British and other Eurosceptics. Prime Minister David Cameron has been clear in his opposition to Mr Juncker for the top job in the Commission - but the argument made by Bild is nothing to do with this. It is about whether the current system of transparency is the right one.