Voting began on Sunday and will continue on Monday in the first election since the COVID-19 pandemic hit the country.
The referendum will decide whether parliament is cut from 945 members to just 600, with the lower house being cut down to 400 parliamentarians and the Senate to 200.
The constitutional amendment was already approved by parliament and if confirmed, would take effect in 2023 during the next elections.
The vote was originally scheduled for May but was delayed due to the COVID-19 pandemic, which has killed more than 35,000 people in Italy.
The latest polls show that many Italians are in favour of the cut to parliament.
Meanwhile, critics of the constitutional reform say it produces minimal cost savings and risks undermining the democratic system by weakening the authority of the parliament.
Italians have also begun voting locally to elect 1000 mayors and seven regional governors, in another election that was delayed due to the pandemic.
The main national governing parties – the Five Star Movement (M5S) and the centre-left Democratic Party (PD) – are bracing for a poor showing in the first electoral test since the outbreak of the new coronavirus.
The right-wing coalition led by former interior minister Matteo Salvini is likely to confirm strongholds in two regions, according to polls. Three other regions could move to the right.
The PD is confident of victory only in Campania, the region around Naples, and is desperate to avoid defeat in Tuscany, a former left-wing stronghold where the League’s candidate could achieve a historic win.
Voting continued until 11:00 pm on Sunday and will resume on Monday morning at 7:00 am until 3:00 pm, Italian media reported.
Results are expected to be announced later on Monday.
Voters at polling stations are required to wear masks and maintain physical distancing as a precaution against the coronavirus.
Once inside, voters may lower their masks just long enough to confirm their identity against voting cards and ID documents.
Furthermore, voters leaving the voting booths will place the ballots inside the boxes themselves, instead of turning them over to poll workers.
