Silvio Berlusconi's supporters threatened "a full-blown rebellion" after the former Italian prime minister was found guilty of publishing illegally obtained wiretaps and given a one-year jail sentence.
The information, which concerned the acquisition of an Italian bank, was published in 2006 in a newspaper owned by the billionaire businessman's family in an attempt to smear the opposition before elections.
The taped conversations created the impression that the then-head of the main centre-Left party had exerted improper pressure over the takeover of a bank by Unipol, an insurance company.
The conviction added confusion to an already chaotic political scene. The country's three main parties are in deadlock after an inconclusive general election result last week.
MPs from Mr Berlusconi's People of Freedom Party claimed that the conviction was the latest example of hounding by supposedly Left-wing judges.
"Expect a rebellion against this way of administering justice," said Sandro Bondi, a senior member of the party.
"At this rate, the country will mount an open rebellion, a civil and democratic rebellion, but a full-blown rebellion nonetheless."
Renato Brunetta, a minister in Mr Berlusconi's last conservative coalition, described the verdict as "really intolerable persecution which has nothing to do with justice".
Mr Berlusconi (76), who is trying to engineer a role in a grand coalition, said he was stunned by the verdict and repeated previous claims that he had been subjected to a witch-hunt by biased courts.
"It is really impossible to tolerate judicial persecution of this kind which has been going on for 20 years and which re-emerges every time there are complex moments in the political life of our country," he said.
Mr Berlusconi has an automatic right to two levels of appeal, during which time the sentence is suspended, meaning he is unlikely to go to jail.
(© Daily Telegraph, London)