The Italian government on Wednesday won the first of three confidence votes on a fiercely contested electoral law that is likely to penalise the anti-establishment 5-Star Movement in next year's national election.
The proposed voting system is backed by three of the country's four largest parties, with the centre-left government looking to rush it onto the statute books ahead of elections, which are due by May 2018.
Five-Star supporters protested in front of parliament as the Chamber of Deputies voted on the bill, which passed easily by 307 votes to 90. The maverick movement's deputies did not take part in the vote to show their dissent.
Unlike the current rules, the new system would allow the formation of multi-party coalitions before the ballot, a factor likely to hurt 5-Star, which is topping most opinion polls and refuses to join alliances.
"They want to take away our right to choose," said Nicola Zuppa, 45, who said he had paid 175 euros ($200) to travel from Padua in northern Italy to take part in the protest, which drew up to 2,000 people in the heart of Rome.
A second confidence vote will be held later on Wednesday and a third one is set for Thursday, as the ruling coalition looks to truncate discussion on the bill and sidestep dozens of planned secret votes on various amendments.
A final secret vote on the bill, in which lawmakers could break with the party line, is scheduled before the end of the week. If it passes, the law moves to the upper house Senate.
"If you allow the electoral rules to be changed again so that the scum of the country rises to the top yet again, it will be your children who pay the price," 5-Star's founder Beppe Grillo wrote on his blog on Wednesday.
President Sergio Mattarella, the only figure with the power to dissolve parliament, has called for new voting rules because the current system is very different for the upper and lower houses, meaning it could throw up conflicting majorities.
All previous attempts to harmonise the rules have failed, most recently in June when dissident deputies used a secret vote to upend part of the proposed legislation.
Former Prime Minister Matteo Renzi's Democratic Party (PD) drafted the latest version, which is supported by right-wing parliamentary rivals Forza Italia (Go Italy!) and the Northern League. Five small parties are also backing the proposed law.
"This electoral law is supported by eight different parties, and it's a very delicate equilibrium," said Ettore Rosato, the PD group leader who presented the bill, which is called the 'Rosatellum' after him.
Five-Star estimates that the new rules could cost it up to 50 seats in the Chamber of Deputies and potentially scupper its chances of being the largest group in parliament after the vote.
Mattarella is expected to give the formation that gets the most seats the first crack at forming a government.
The ruling Democratic Party denies the new rules are designed to penalise 5-Star.
"No one is preventing (5-Star) from making alliances if they want to," Rosato told reporters. "If they don't want to do them, they can continue to be an isolated party."