European Parliament President Martin Schulz said the European Union should revise its code of conduct after the furore caused by former European Commission President Jose Manuel Barroso taking a job with US bank Goldman Sachs, a German paper reported today.

"We should adapt the code of conduct to make it clearer what former EU Commission presidents and EU commissioners are permitted to do," Schulz told the German newspaper Die Welt in an interview.

Barroso's successor Jean-Claude Juncker on Sunday opened an unprecedented ethics investigation of Barroso and whether he had breached a requirement to act with integrity by taking the job with the US investment bank.

Goldman appointed Barroso as a non-executive chairman of its international arm in London two weeks after Britons voted for Brexit in June. Barroso said he would advise the bank on issues arising from the negotiations for Britain to leave the European Union.

An independent panel of senior former EU figures, including a judge and a member of parliament, will review the case, which the Commission has previously said did not appear to breach its code of conduct as Barroso had been retired for over 18 months.

The uproar over him joining an American institution held partly responsible by many Europeans for a financial crisis that nearly broke the euro, comes as the EU is battling in the wake of Britain's vote to leave the bloc in June to dispel public perceptions that it is a technocratic pawn of global capital.

Asked if the current EU ethics rules were too lax, Schulz told the paper, "They are not precise enough. It's normal when a former EU Commission president is looking for a job. No one has an issue if he writes books or teaches at a university. But it's strange that Barroso wants to advise the biggest investment bank on the Brexit issue."

Barroso has accused Juncker of "discriminatory" behaviour for opening the ethics probe and said the inquiry was "inconsistent" with the treatment of other former commissioners.