Institutional and retail investors are taking the National Australia Bank to court for losses linked to the subprime mortgage crisis.
The 250 shareholders are claiming to have lost around $A450 million because the bank did not adequately inform them of the investment risk.
The ABC reports law firm Maurice Blackburn lodged the class action on Thursday in the Victorian Supreme Court.
In 2006, National Australia Bank bought more than $A1 billion worth of very complex debt related bonds called collateralised debt obligations.
When the subprime crisis hit, the value of these investments plunged dramatically.
Maurice Blackburn argues that NAB should have known about the volatile market conditions and about the troubles in the US housing market and warned investors earlier.
The NAB is the parent of the BNZ.