By Roberto Landucci
ROME (Reuters) - The Italian government has put its bitterly contested electoral reform to a confidence vote in parliament, forcing rebels in Prime Minister Matteo Renzi's Democratic Party (PD) to back him or face new elections.
The announcement by Institutional Reform Minister Maria Elena Boschi angered opposition politicians, who accused Renzi of a "fascist" power grab and hurled abuse at government ranks.
Three separate confidence votes on different sections of the bill are expected between Wednesday and Thursday.
If they all pass, the reform will become law, ending more than a year of parliamentary debate. But if Renzi loses any of the three ballots, he will have to hand in his resignation to President Sergio Mattarella, who would have to appoint a new government or else call fresh elections.
PD party rebels suggested that they would shun the ballots rather than actually vote against their own government, making it more likely that Renzi will win the confidence motions.
In combination with a separate shake up of the Senate, the new law, dubbed the "Italicum", is designed to leave a clear winner after a general election by awarding a generous "majority premium" to the leading party.
Critics say the bonus is excessive and undemocratic. They are also unhappy about provisions that would let party chiefs handpick some candidates, saying they would concentrate too much power with the leadership.
But Renzi, the dominant figure in Italian politics since seizing power last year, said that after years of revolving-door governments, the law had to be changed. He challenged the opposition and dissidents in his own party to take him on.
"The lower house has the right to get rid of me if it wants, that's what a confidence vote is for. As long as I'm here, I will try to change Italy," he tweeted after the announcement.
PD traditionalists, who resent the iconoclastic approach that has earned Renzi the nickname "Demolition Man", sharply criticised the fast-talking premier's decision.
Pier Luigi Bersani, a former centre-left leader and prominent opponent to Renzi within the PD, said on Twitter: "A government does not hold a confidence vote on democracy. This is creating a worrying precedent."
Renzi has a majority of around 70 seats in the lower house or Chamber of Deputies which would be at risk if all the PD rebels voted against the bill.
However, with the PD rebels heavily divided themselves, it remains unclear how many are ready to vote against Renzi, who has so far faced down attempts to derail his reform package.
Former prime minister Silvio Berlusconi, who originally cooperated with Renzi on the reform, has withdrawn support.
"We will do everything we can to prevent Renzi fascism," the floor leader of his Forza Italia party, Renato Brunetta, said.
Deputies from the leftist SEL party threw chrysanthemums onto the floor of parliament and said they were witnessing "democracy's funeral". Fabiana Dadone, floor leader of the anti-establishment 5-Star Movement, compared Renzi to fascist leader Benito Mussolini.
If the bill is approved, it will only take effect in July 2016.
(Writing by James Mackenzie; Editing by Crispian Balmer)