Factbox: How Italy's new electoral law works

ROME (Reuters) - Italy's parliament on Monday approved a new electoral law pushed through by Matteo Renzi's government despite furious objections from all the opposition parties and a minority of Renzi's ruling Democratic Party. Renzi says the law will guarantee a clear winner at elections, providing political stability and ending the backroom horse trading between parties often needed to form coalition governments in Italy. Opponents complain it concentrates too much power in the hands of the winning party and does not allow voters to directly choose their representatives. Following are the main aspects of the new law: * The system is based on proportional representation. Multiple candidates from party lists are elected in 100 constituencies nationwide. However national party bosses decide the lead candidate on each list, effectively giving them control over most of the deputies who are elected to parliament. At least 40 percent of their lead candidates must be women. * Parties that get less than 3 percent of the vote are excluded from parliament. If the winning party gains at least 40 percent of the vote, it gets a winner's bonus that automatically gives it 340 seats in the 630-seat Chamber of Deputies. * If no party wins 40 percent, a run-off ballot between the two largest parties is held two weeks after the first election to determine which party gets the winner's bonus. * The law only takes effect from July 2016, in order to give Renzi time to pass a separate reform of the upper house Senate. He wants to abolish the Senate as an elected chamber and turn it into an assembly with reduced powers made up of mayors and regional councillors. The new electoral law, which only applies to the lower house of parliament, cannot be used until the reform of the Senate is completed. (Reporting By Gavin Jones)