Marc Tarabella, a 59-year-old old socialist, has been held in pre-trial detention since February 11. He has accused judge Michel Claise of bias, demanding he step aside.
Tarabella protests he is innocent, but has been remanded in custody as Claise builds his case against several suspects, including another MEP and a handful of lobbyists and parliamentary assistants.
On Tuesday he was permitted to attend a hearing in Brussels while his lawyer, Maxim Toller, argued that the case makes leaps beyond the available evidence to paint a picture of guilt.
Claise and the federal prosecutor's office deny the claim and the Brussels appeals court is expected to decide whether or not he can remain on the inquiry on March 14.
EU policy chief Josep Borell is quoted by Reuters as saying the European Union maintains a position of “zero tolerance” of corruption and will wait for the results of the decision of a judicial investigation into the case."