Allies quick to accuse Socialist Government of Francois Hollande of conducting a witch-hunt.
Former French President Nicolas Sarkozy has been charged with corruption and influence peddling in a criminal investigation.
The decision came after Sarkozy was questioned for 15 hours, marking the first time a French head of state has been taken into custody.
Sarkozy turned himself in for questioning in an inquiry that could torpedo his hopes of making a political comeback.
His allies accused the Socialist Government of President Francois Hollande of conducting a witch-hunt against the politician many on the right hope will run again for the presidency in 2017.
Sarkozy arrived in a black saloon car with tinted windows to be questioned by investigators in Nanterre, west of Paris, in one of a number of corruption inquiries embroiling him since he was defeated by Hollande in 2012.
The interrogation followed the arrest on Tuesday of Sarkozy's lawyer and two senior judges under investigation for allegedly trying to obtain information about legal cases against the former President.
Police are trying to establish whether Sarkozy promised a plum job in Monaco to a judge in return for letting him know whether corruption allegations against him - regarding irregularities in his victorious 2007 election campaign - would go to court. Sarkozy, 59, denies all wrongdoing in this case and in all the others in which he is implicated. He faces five years in prison and a fine of 500,000 ($780,900) if charged and convicted in the current case in which he is suspected of the crime of "influence peddling".
French media in March disclosed police intercepts of Sarkozy's telephone conversations with his lawyer, Thierry Herzog, which suggested the two men may have persuaded a judge to provide inside information on a case against the former President.
The phone taps had initially been ordered by judges investigating allegations that Libya's Muammar Gaddafi had donated up to 50 million in illegal financing for Sarkozy's 2007 campaign.
After four fruitless months the judges discovered Sarkozy had a secret phone registered under an assumed name. Recordings from that led to the opening of the influence peddling investigation.
Sarkozy was cleared last year of taking envelopes stuffed with cash from France's richest woman, Liliane Bettencourt, the L'Oreal heiress.