By Gavin Jones and Steve Scherer
ROME (Reuters) - Several hundred supporters of Italy's 5-Star Movement chanted slogans and waved flags in front of parliament on Wednesday to protest an electoral law that is likely to penalize the maverick party ahead of next year's national election.
The new law, which would be used in a national election due by next May, is backed by three of the four largest parties plus a handful of small ones.
Unlike the current rules, the new system would allow the formation of multi-party voting coalitions before the ballot, a factor likely to hurt 5-Star, which 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 Padova in northern Italy to take part in the protest.
Five-Star supporters distributed leaflets declaring a "full democratic emergency" on commuter trains early on Wednesday to try to muster a large crowd in the middle of a work day ahead of two confidence votes on Wednesday, both of which the government is expected to win comfortably.
"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.
Small left-wing parties that oppose the law will also stage a protest in front of the ancient Roman Pantheon temple in the afternoon.
Opponents are particularly enraged that the government is putting the electoral law to votes of confidence that truncate discussion, amendments and secret votes on the legislation.
If the government loses a confidence vote, it is obliged to resign. The first vote will begin at 3:45 p.m. (1345 GMT).
A third confidence vote on will be held on Thursday, to be followed by a final secret vote in which lawmakers could break with the party line. If it passes, the bill moves on to the upper house Senate.
Matteo Renzi's ruling center-left Democratic Party (PD) drafted the bill, which is supported by right-wing parliamentary rivals Forza Italia (Go Italy!) and the Northern League. Five other small parties are also backing the proposed law.
"This electoral law is supported by eight different parties, and it's a very delicate equilibrium," Ettore Rosato, the PD group leader who presented the bill (dubbed the Rosatellum after him), said on Wednesday.
Five-Star estimates that the new rules could cost it up to 50 seats in the Chamber of Deputies, the lower house and potentially scupper its chances of emerging as largest group in parliament after the vote.
President Sergio Mattarella is expected to give the formation that gets the most seats in parliament the first crack at forming a government.
The ruling Democratic Party denies the new rules are designed to penalize 5-Star.
"No one is preventing (5-Star) from making alliances if they want to," Rosato told foreign journalists. "If they don't want to do them, they can continue to be an isolated party."
(Additional reporting by Steve Scherer; Editing by Alison Williams)