The Laudani clan, part of Sicily's 'Cosa Nostra' crime syndicate, was found to have infiltrated several commercial enterprises in Italy's wealthiest city - including budget supermarket Lidl.
Four of Lidl's ten management sections in Italy were handed over to State control over suspected mafia infiltration, though the chain itself is not suspected of wrongdoing.
In total, the four sections - located in Lombardy, Piedmont, and Sicily - run around 200 stores across the country.
Milan judge Ilda Boccassini said the case showed "an evolution of the system of corruption in Italy" and that "corruption is rampant in Milan".
"They knew the right people to bribe," she said.
The clan set up companies in the logistics and private security sector, and won contracts to work for Lidl, other commercial businesses, schools, and even a Milan court.
The announcement came on the same day that anti-mafia police busted a mafia group in the south of the country, believed to have made millions through its involvement in running a migrant reception centre.
A total of 68 people were arrested in that operation, accused of syphoning of EU funds destined for migrant care.