Authorities in Brussels have charged HSBC's private banking arm, which is based in Switzerland, with helping wealthy Belgians to avoid taxes.
Prosecutors allege that hundreds of clients - including diamond dealers in Antwerp - moved money to offshore tax havens with the help of the bank.
They said it resulted in hundreds of millions of euros in lost tax revenue.
In August, HSBC warned that the penalties in relation to such allegations "could be significant".
