The row broke out in the Chamber of Deputies as Berlusconi, battling to stay in power, hit back after a humiliating grilling from anti-corruption magistrates by saying their investigation into him formed part of a political "coup d'etat."
The argument erupted when the Northern League broke with other coalition parties and voted with the opposition to set up a commission to review Italian broadcasting.
Berlusconi's huge media interests, including three television stations, have been a constant source of friction with the combative League, which now says the stormy seven-month-old coalition has come to the end of the line.
The League's vote had members of Berlusconi's Forza Italia and the far-right National Alliance screaming insults at their nominal allies and chanting "resign" at Speaker Irene Pivetti, a member of the League.
"What we are witnessing today is the birth of a (new) majority in parliament that rides roughshod over the rules," said Ignazio La Russa of the National Alliance.
League leader Umberto Bossi fired another shot across the coalition's bows by drafting a motion that amounted to a virtual statement of no-confidence in Berlusconi and his justice minister, Alfredo Biondi.
The motion has yet to be accepted for debate, but it accuses Biondi of attempting to block the magistrates' inquiry into Berlusconi for alleged corruption.
The bombshell probe, the first criminal investigation into a serving Italian prime minister, has strained Berlusconi's fractious center-right coalition to breaking point."The Berlusconi chapter is closed. ... We think the government is finished," Marco Formentini, League mayor of Milan, told reporters. "It's time to think of a new political alliance."
Berlusconi, propelled to power in elections in March on promises to clean up Italy, was quizzed for seven hours by "Clean Hands" investigators in Milan on Tuesday over suspicions that he knew of bribery in his Fininvest business empire.
He went on television after the meeting to say investigators had no evidence against him and pledged to stay in office.
"The conspiracy against me and my government is so vast and intense that it can be likened to a coup d'etat," he told La Repubblica newspaper on Wednesday.
He is suspected of knowing that three companies in his media-to-retailing empire paid tax police 330 million lire ($205,000) in bribes in 1990 and 1991 for lenient audits.
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