Maurice Blackburn Lawyers is pursuing a potential legal action against CBA over a share price fall connected to alleged breaches of anti-money laundering and counter-terrorism financing laws.
Maurice Blackburn national head of class actions Andrew Watson said it loomed as Australia's largest shareholder class action, but did not specify the potential amount.
CBA had admitted its board was aware of the breaches in the second half of 2015 but the bank said nothing to the stock exchange until August 4 this year, he said.
The period of alleged misconduct amounted to almost two years and the bank's stock was probably the most heavily traded on the stockmarket.
"On any view it's going to be a very large claim," Mr Watson said in Melbourne on Wednesday.
Regulator AUSTRAC has launched civil proceedings accusing CBA of systemic failure to comply with anti-money laundering and counter-terrorism financing laws.
Australia's largest bank has blamed a coding error and admitted it discovered and fixed the error in 2015.
Maurice Blackburn says CBA's 800,000 shareholders suffered a significant share price drop on the back of news of the AUSTRAC proceedings.
The class action, however, is only open to shareholders who bought CBA shares between August 17, 2015, and August 3 this year, and who still held some stock on the afternoon of August 3.
Mr Watson said that amounted to thousands upon thousands of shareholders.
"I'd anticipate that we will have very large levels of interest from institutions and from retail shareholders."
The class action is being backed by litigation funder IMF Bentham.
