Embattled Bank of Italy governor Antonio Fazio is being investigated for alleged insider trading.
The investigation is part of a wider probe into a banking scandal involving Banca Popolare Italiana's (BPI) failed takeover bid for Banca Antonveneta.
Mr Fazio had already been accused of abusing his position in trying to keep Banca Antonveneta out of the hands of rival bidder, Dutch bank ABN AMRO.
But he has so far ignored widespread calls for his resignation.
The former chief of BPI, Gianpiero Fiorani was arrested earlier this week.
He is in prison awaiting questioning over allegations of embezzlement, market rigging and money laundering.
To date, the Italian government has said that only the central bank's Superior Council, most of whose members were appointed by Mr Fazio, can remove the governor.
- 185 Corruption