Maurice Blackburn lawyers will be representing about 250 institutional and retail investors in the class action, filed in the Victorian Supreme Court on Thursday.
The action claims NAB failed to disclose its exposure to the subprime mortgage market in 2007 and 2008.
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"Shareholders who bought shares before NAB revealed its true position suffered losses as a result," Maurice Blackburn principal Andrew Watson said in a statement on Thursday.
NAB shares slumped 45 per cent during 2008 as the subprime crisis hit markets around the world and financial stocks in particular.
NAB wrote down $1.5 billion during 2008 related to the bank's $4.5 billion exposure to debt conduits.
The debt instruments comprise infrastructure debt, commercial property, collateralised loan obligations (CDOs) and synthetic CDOs linked to the US subprime crisis.
