Agriculture, construction workers paid 40 per cent less than Italians in similar jobs
The investigation found migrant workers in the agriculture and construction sectors in areas of southern Italy were paid 40 per cent less on average than Italians doing the same job and were often paid below the legal minimum.
In some cases workers were not paid at all or their pay was arbitrarily withheld.
Italy has borne the brunt of irregular sea-borne migration to southern Europe, which has risen with unrest in North Africa and the Middle East.
Migrants, who say they are attracted by the prospect of a better life in Europe, often risk the voyage across the Mediterranean in overcrowded fishing boats. Thousands have died from shipwrecks, harsh conditions at sea or a lack of food.
The Amnesty report said that stringent Italian immigration laws, which criminalize irregular entry to the country, made migrant workers more vulnerable to exploitation because they cannot complain to authorities for fear of arrest.
"The outcome for migrant workers is often: wages well below the domestic minimum, arbitrary wage reductions, delays in pay or no pay at all, and long working hours," Amnesty researcher Francesca Pizzutelli said in a statement.
"While the authorities in any country are entitled to control immigration, they must not do so at the expense of the human rights of all people in their territory, including migrant workers."
The report, which noted that racism against migrants was a problem, focused on "severe" exploitation of workers from sub-Saharan Africa, North Africa and Asia in the agricultural sector in Latina and Caserta in Italy's south.
It recommended that Italian authorities develop a way for migrant workers to safely lodge complaints against employers.
One Indian migrant, speaking anonymously to Amnesty, said that he had agreed to work seven days per week for about three euros per hour or 700 euros per month, but that his employer had instead been paying him just 100 euros per month for the last seven months.
"I can't go to the police because I don't have documents: they would take my fingerprints and I would have to leave," he was quoted as saying in the report.
Amnesty also investigated the aftermath of violent clashes that broke out in the small agricultural town of Rosarno when workers marched through the town to protest discrimination and poor living conditions in 2010.
Tension rose this weekend when the mayor of San Ferdinando, a town adjacent to Rosarno, ordered the eviction of a "tent city" of migrant workers, leaving 1,000 homeless, according to Italian media.
Of Italy's estimated 5.4 million foreign nationals, about half-a-million had no valid documentation, the report said.