Five former Deutsche Bank top managers are being investigated by a prosecutor in Trani, southern Italy, including its ex-chief executive Josef Ackermann, consumer associations Adusbef and Federconsumatori said after filing their legal complaint.
They accuse Deutsche Bank of selling "massive" amounts of Italian government debt between January and June 2011 while publicly stating that the Italian debt situation was "sustainable".
This they said, had "altered the normal price formation in the government debt market".
The time of the sales coincided with Italy's debt crisis, which eventually led to the fall of Silvio Berlusconi's government, making way for Mario Monti.
Police have already seized documents and emails at the Milan branch of the German bank in the investigation, they said.
Deutsche Bank said it was fully cooperating with the authorities in the matter, adding that it had submitted information and documents to stock exchange watchdog Consob as early as 2011 in a related inquiry.