The April 2006 general elections were highly contested. Former prime minister Romano Prodi led a center-left coalition, l’Unione (the Union), to win a narrow victory in the voting. Berlusconi disputed the outcome, however, leading to a court review of about 5,000 contested ballots. The Supreme Court of Cassation subsequently confirmed Prodi’s victory, announcing a final margin in the lower house of parliament of fewer than 25,000 votes out of more than 38 million cast. The Union coalition, comprising nine parties, took 348 of 630 seats in the Chamber of Deputies. The coalition also claimed a razor-thin victory in the Senate, winning two more seats than the center-right coalition led by Berlusconi. Prodi formed a coalition government and was officially confirmed as prime minister in May.

Prodi and his center-left coalition strongly opposed sweeping reforms to the 1948 constitution that had gained parliamentary approval under Berlusconi. In a referendum held in June 2006, voters resoundingly rejected the proposed reforms, which would have greatly increased the powers of the prime minister and given more autonomy to the country’s 20 regions.