Italians go to the polls on Sunday to vote on a controversial constitutional referendum, which has also become a confidence vote for the country's Prime Minister, Matteo Renzi.

Opinion polls show voters are leaning towards voting down Renzi's planned constitutional reforms, but many Italians say they still don't know which way they will vote. If passed, the referendum would drastically curb the role of Italy's upper house Senate.

Renzi says that would streamline the government and simplify the legislative process. But opposition lawmakers say the proposed law would only complicate government affairs. Renzi has threatened to resign if the referendum doesn't pass.