France has called on the former head of the European Commission, Jose Manuel Barroso, not to take up a job advising US bank Goldman Sachs on Brexit.
French Europe Minister Harlem Desir called the move "scandalous" and said it raised questions about the EU's conflict of interest rules.
Ex-commissioners are free to take up a new role 18 months after leaving.
Despite accepting the job after 20 months, Mr Barroso has come under fire for ignoring the spirit of the rules.
Mr Desir drew attention to the ill-timing of the job with Goldman Sachs.
"It's a mistake on the part of Mr Barroso and the worst disservice that a former Commission president could do to the European project at a moment in history when it needs to be supported and strengthened," he told the French parliament, referring to Europe's shock after Britain voted to leave the EU on 23 June.
The bank hired Mr Barroso as an adviser and non-executive chairman of its international business, with a brief of advising the bank on the consequences of Brexit.
Mr Barroso has said he hopes to bring his EU experience to bear as the bank's London operation deals with Britain's imminent negotiation of withdrawal from the EU.
In his new role, Mr Barroso will be able to draw on his intimate knowledge of the EU and have access to many officials and politicians he worked with at the European Commission.
'It doesn't surprise me'
Mr Desir's attack in the French parliament was the latest in a sustained tirade against Mr Barroso's appointment, with some calling it "shameful".
French Finance Minister Michel Sapin told reporters on Tuesday "If you have loved Europe, you shouldn't do this to it, especially not now," adding: "But this doesn't surprise me from Mr Barroso."
Who is Jose Manuel Barroso?
- Conservative ex-premier of Portugal
- President of the European Commission, the EU's executive arm, from 2004-2014
- As Commission head he was at heart of the banking crisis and the fallout within the Eurozone
- Has said in the past Britain could not negotiate with the US and China "on an equal footing" on its own
The European Ombudsman has called for the EU to tighten rules on commissioners taking appointments after leaving office.
Ombudsman Emily O'Reilly said adhering to technical rules did not absolve former staff of a wider duty to show integrity.
"Any suggestion that the spirit of the law is being ignored risks undermining public trust in the EU," she said.