Brazil's Supreme Court was scheduled Wednesday to start considering a demand by President Michel Temer for the recusal of the chief prosecutor leading a corruption case against him.
Temer's lawyers argue that the prosecutor general, Rodrigo Janot, is mounting an "obsessive persecution" and that he is "greatly exceeding the constitutional and legal limits."
This comes as Janot is expected to file criminal charges against Temer before he leaves his post and hands over to a new chief prosecutor on Monday. Janot is expected to charge Temer with obstruction of justice.
Congress has to approve any trial of the president and in August voted overwhelmingly to toss out a first charge, which accused Temer of taking bribes. Temer is believed to retain sufficient support to ride out a second charge.
The obstruction of justice charge would depend in part on a secret recording made by meatpacking billionaire Joesley Batista in which Temer allegedly is heard calling for payments to a jailed politician to prevent him testifying.
Batista and his brother Wesley signed plea deals with prosecutors after admitting they had run a huge bribery network to benefit their company JBS.
However the leniency accord has been torn up after Joesley Batista was accused of withholding information from prosecutors.
In another motion, Temer's lawyers are asking the Supreme Court to block any new criminal charges by Janot until clarification of what they say are irregularities in the way the Batista plea bargain evidence was collected.
The court was due to meet at about 1700 GMT but it was not clear whether the Janot-related items would be considered quickly, with delays potentially pushing the matter to another day.