Wikipedia's Italian edition has taken all entries but one offline in protest at a draft privacy law restricting the publication of police wiretaps.
Transcripts of his telephone calls have embarrassed Prime Minister Silvio Berlusconi, on trial for corruption and using underage prostitutes.
The draft law would oblige websites to amend content within 48 hours if the subject deems it harmful or biased.
Italian protesters wearing gags gathered outside parliament in Rome.
MPs have begun debating an amendment which would limit the right of newspapers and other websites to publish wiretaps during a police investigation.
'Restriction of freedom'
Wikipedia says it may take down its Italian site, www.wikipedia.it, permanently if the law is passed. Amendments would have to be published within 48 hours at the request of the person making the complaint, without any recourse to a court or independent adjudicator.
In an open letter to its Italian readers, Wikipedia said: "The obligation to publish on our site the correction... without even the right to discuss and verify the claim, is an unacceptable restriction of the freedom and independence of Wikipedia."
Mr Berlusconi has said the law - which has been making its way through parliament for more than a year - is needed to protect the rights of private citizens.
Last month, Italian news sites published transcripts of Mr Berlusconi's phone conversations, recorded during an investigation into whether the prime minister was being blackmailed by a businessman who claimed he procured prostitutes for Mr Berlusconi's parties.
In one, he derided Italy and said he wanted to leave the country. In another, he used a crude insult to describe German Chancellor Angela Merkel.
Mr Berlusconi denies all the charges against him, saying he is the victim of left-wing magistrates determined to force him from office.
He began trying to tighten Italy's privacy laws soon after he was re-elected in 2008.