The referendum would provide for the definitive abolition of Italian provinces — a level of governance below that of the regions — and transfer some powers now overseen by the regions — like civil protection, strategic infrastructure and energy, and major transportation — to the central government in Rome, mostly reversing a change undertaken more than a decade ago, which devolved power to the regions.

The referendum would abolish a national council on the economy and labor that advises the government and Parliament. It would tweak the process for electing judges to Italy’s highest court and its governing body, as well as the procedures for electing the president of the republic, who serves as head of state. It would also make it easier for citizens to propose legislation.

Each article has been the subject of intense debate. In broad terms, supporters say they believe that the changes will help streamline Italy’s sclerotic legislative process, where laws can take months, if not years, to get passed.

Opponents say the changes will concentrate too much power in the hands of the government, a risk that the drafters of the Constitution, written a few years after the downfall of Mussolini’s fascist government, wanted to avoid. Many opponents argue that proposed overhaul of the Senate is too complicated, creates more problems than it will solve, and will grant parliamentary immunity to regional officials, a privilege they do not have.

Why is the referendum on national issues so controversial?

When Mr. Renzi, who took office in a party coup in 2014, was riding high in the opinion polls, he staked his administration on the outcome, vowing to step down should his overhauls be rejected. But since then, his popularity has fallen, and his opponents have jumped on the referendum as a means by which to topple the government. Many polls suggest that the referendum could be seen as a litmus test for the Renzi government — a big risk for the prime minister.