By Christian Fraser
BBC News, Rome
Italians are voting in a referendum on Sunday and Monday to decide whether to give new powers to the prime minister and the regions.
PM Romano Prodi (L) is deeply opposed to the bill
The bill to change the constitution was put forward by the previous government of Silvio Berlusconi.
At stake is a bigger say for local government in how taxes are spent.
New Prime Minister Romano Prodi is deeply opposed to the bill. His centre-left coalition has been campaigning for a "No" vote.
The bill was sponsored by the populist Northern League party, who have long campaigned for devolved power.
Their leader, Umberto Bossi, has made the progression of the bill a prerequisite for his continued support of Mr Berlusconi.
If it is defeated, there is the prospect the Northern League will split from the centre-right coalition - a move that would undermine Mr Berlusconi's leadership of the opposition.
Italy has had 61 governments since 1945. Supporters of this bill say it would give greater stability to the Italian government.
The prime minister would be granted powers to dissolve parliament, appoint and dismiss ministers and determine the general direction of government policy.
Berlusconi's leadership of the opposition may be at risk
These were all powers that were deliberately kept out of the hands of the prime minister in the 1948 constitution, as a way of preventing the emergence of another figure like fascist dictator Benito Mussolini.
The bill would also redefine the role of Italy's two parliamentary chambers.
The lower house - the Chamber of Deputies - would take the dominant role in matters of national interest like foreign policy, defence and immigration.
The upper house - the Senate - would become responsible for federal law.
But most significantly this bill would give greater autonomy to Italy's 20 regions.
They would gain control over education, healthcare and law and order, and would win special representation in the nation's supreme court.
Some estimates say regional government would take control of around 40% of public expenditure.
There is no quorum needed for a constitutional referendum, which for the "Yes" camp is perhaps just as well.
KEY POINTS OF REFORM
Most radical shake-up since constitution introduced in 1948
Strengthens prime minister's powers, allowing him to dissolve parliament
Cuts president's powers
Twenty regions would get autonomy over education, health and local policing
Cuts number of representatives in both chambers
Parliament approved changes by a simple majority last November
This is the third time in as many months that Italians have gone to the polls.
Experts say there is unlikely to be a very big turnout.
The polls show there is little support for the proposals, but it could swing on who gets their vote out.
There is no doubt reforms are needed here, but there are many who say this bill needs greater thought.
Vannino Chiti, Mr Prodi's minister for institutional reforms, called the proposals "an awful mess".
"We would end up with 20 regional health systems, 20 regional school systems, and all sorts of divisions among Italians," he says.
In short - divisions between north and south. The poorer regions in the mezzogiorno are hugely dependent on tax money that comes from the north.
Italians have already been to the polls twice in three months
Two studies done here last year, by groups looking at child health, found that if the south were independent it would be the poorest of the 25 EU members in terms of per capita national income.
And the changes could lead to disparities in the quality of public services.
There is a fear that teachers and health professionals might desert the south, preferring better wages and prospects in the north.
One of the other main arguments against the reforms is the cost.
Italy urgently needs to cut its budget deficit. The proposals risk adding expensive layers of bureaucracy to a system of public administration where there is already plenty of waste.