Critics accuse the new National Guard of echoing Mussolini's Fascists
Italy's parliament has given final approval to a law criminalising illegal immigration and allowing citizens' patrols to help the police keep order.
The new measures have been strongly criticised by human rights groups and the Vatican.
Illegal immigration will be punishable by a hefty fine and those who knowingly house illegal migrants will face up to three years in prison.
The law also extends detention periods for illegal migrants to six months.
It was passed in the Senate (upper house) on Thursday, with 157 in favour and 124 against. The lower house passed it in May.
The unarmed citizens' patrols are among the most controversial measures.
A right-wing uniformed group called the Italian National Guard was set up last month, likened by some to Benito Mussolini's Fascists. It vowed to start patrolling the streets.
But Interior Minister Roberto Maroni said the group, which sports beige uniforms and black military-style hats, would not be allowed to mount street patrols.
Mr Maroni, a member of the anti-immigration Northern League, has steered the legislation through parliament.
The party is a key ally of Italy's right-wing Prime Minister Silvio Berlusconi, and made tougher measures against immigration a condition of its support for his re-election last year.
The new law makes illegal immigration punishable by a fine of 5,000 to 10,000 euros (£4,276 - £8,553).
It also requires parents registering a birth to present documents proving that they are legal residents.
Opposition senators held signs calling the government "the real clandestines"
Italy has just introduced a policy of returning boatloads of migrants to Libya before they can claim asylum.
The government says it faces an unmanageable flood of immigrants, many arriving on outlying islands which do not have the means to cope.
More than 36,000 migrants landed on the shores of Italy last year - an increase of about 75% on the year before.
Critics say the government is targeting especially immigrants and Roma (Gypsies).
The Vatican said the new law was "focusing on crime and leaving integration completely out of the picture".