A Brazilian Supreme Court judge on Friday blocked ex-president Luiz Inacio Lula da Silva from becoming presidential chief of staff and sent the corruption case against him back to criminal court.
The preliminary injunction, a heavy blow for embattled President Dilma Rousseff, applies until the full Supreme Court can rule on the legality of her controversial decision to appoint her predecessor and mentor to head her cabinet.
A flurry of court challenges were filed in the wake of Lula's appointment, alleging his nomination was aimed at saving him from arrest in an explosive probe into a multi-billion-dollar corruption scam at state oil giant Petrobras.
Cabinet ministers in Brazil have immunity from prosecution in criminal court, and can only be tried before the Supreme Court.
Supreme Court judge Gilmar Mendes returned the corruption case against Lula to judge Sergio Moro, the man leading the highly damaging Petrobras investigation.
Mendes said the fact that Lula's appointment had the effect of removing him from Moro's jurisdiction "could amount to an act of fraud against the constitution."
Moro caused an uproar after the appointment was announced when he leaked a wire-tapped phone call between Rousseff and Lula suggesting she appointed him so he would gain ministerial immunity.
Anti-government protests erupted after the release of the recording from Lula's bugged phone, in which the president told him she was sending him a document with his official ministerial appointment, to be used only "if necessary."