Three senior French officials are set to open an inquiry into claims that judges trying former prime minister Alain Juppe suffered a dirty tricks campaign.
Chirac ordered a probe into claims of harassment
The inquiry, ordered by President Jacques Chirac, will examine claims of threats, phone-tapping and break-ins.
Mr Juppe was barred from seeking public office for 10 years after being found guilty of a jobs fraud at Paris City Hall when Mr Chirac was mayor.
Mr Chirac was under investigation over the same affair until 2001, when he successfully claimed the constitution granted him presidential immunity.
Mr Chirac led generous praise of Mr Juppe on Monday, sparking speculation that he wants him to stay on as leader of his Union for a Popular Majority (UMP) Party and try to win his case on appeal.
The president described his protege as a "political figure of exceptional
quality, competence, humanity and honesty".
"France needs men of his quality," he added.
The claims of dirty tricks centre on the court in the Paris suburb of Nanterre, where the trial was held.
Court president Catherine Pierce said on Saturday that judges' offices had been "visited"
before and during the trial, their office computers searched and that their telephones - including personal lines - tapped.
Threats and pressure against the magistrates have also been alleged - and the verdict against Mr Juppe was prepared on a laptop computer to avoid hackers accessing it.
"We don't know who was behind all this. We simply came to the
conclusion that a lot of people wanted to know what would be our
decision," she told Le Parisien newspaper.
A statement from Prime Minister Jean-Pierre Raffarin's office announced that inquiry was being launched.
"If the allegations are proven, that will be a matter of extreme gravity," the statement said.
In two separate moves, the speaker of the National Assembly announced plans for a parliamentary inquiry, and the Justice Ministry started proceedings to establish whether criminal charges could be brought.
One French newspaper suggested that the government inquiry may signal Mr Chirac going on the counter-attack, having realised that the Juppe affair was calling his own record into question.
"What better way out of this implication than to cloak himself in his official role as guarantor of the magistrature's independence?" the left-wing paper Liberation asks.
Juppe, seen as a possible successor to his ageing mentor, said on Monday he would reveal on Tuesday whether he planned to quit as UMP leader and mayor of Bordeaux.
"I have had a good think. I respect the court. Tomorrow, probably
on television, I shall tell the French what I have decided. Till then
I hope you will understand that I am keeping it to myself," he told supporters at Bordeaux City Hall.
If he loses his appeal against the conviction, the most likely successor to Mr Chirac is seen as hardline Interior Minister Nicolas Sarkozy.