Australia's biggest bank, the Commonwealth, vowed Monday to fight what could become the country's largest shareholder class action over alleged breaches of anti-money laundering laws.

The open class action, filed by law firm Maurice Blackburn and litigation funder IMF Bentham in the Federal Court in Melbourne Monday, followed a civil case launched by Australia's financial intelligence agency AUSTRAC in August.

AUSTRAC alleged the bank engaged in "serious and systemic non-compliance" of anti-money laundering laws involving thousands of transactions.

The class action claims CBA neglected its disclosure obligations as a listed company, hurting shareholders who bought its stock.

CBA has more than 800,000 shareholders, with millions more holding stock through pension funds, according to this year's annual report.

In a brief statement, the bank -- Australia's largest firm by market capitalisation -- said it "intends to vigorously defend this claim".

The case specifically names senior CBA executives -- including chief executive Ian Narev -- claiming they had "early knowledge of the AUSTRAC compliance issues which remained undisclosed until this year", Maurice Blackburn said.

Narev has been one of the casualties in the fallout, with CBA announcing he would retire by the end of the 2018 financial year.

The AUSTRAC case also prompted other Australian regulators to launch inquiries into the bank over its handling of the alleged breaches and its organisational culture.

Shares in CBA, which have slipped since the AUSTRAC announcement, edged up by 0.45 percent to Aus$76.62 in mid-afternoon trade.