The Australian Prudential Regulation Authority, known as APRA, has announced it will investigate the Commonwealth Bank of Australia.
In a statement APRA Chairman Wayne Byres said a number of concerns have been raised in relation to the governance, culture and accountability within the CBA group.
And that given CBA's position in the Australian financial system, it is critical that community trust is strengthened.
CBA has had a tumultuous month.
First, Australia's financial intelligence and regulatory agency, AUSTRAC, initiated proceedings in the Federal Court.
They allege CBA was involved in over 53,000 contraventions of anti-money-laundering and counter-terrorism financing laws.
That announcement saw CBA's shares fall by 5.4 per cent.
Corporate regulator ASIC said it would investigate CBA's behaviour, then embattled chief executive Ian Narev announced he'll resign by July next year.
Last week, Maurice Blackburn lawyers said it was pursuing a potential class action for aggrieved investors.
And now APRA will investigate the culture of Australia's largest bank.
Labor leader Bill Shorten says the Turnbull government can't ignore calls for a royal commission.
"Well, here we go again. Yet again another inquiry into a bank. When will the Turnbull government finally do what it knows needs to be done and what the Australian people want which is to have a Royal Commission into our banks."
Treasurer Scott Morrison says any shortcomings will be adequately addressed by both ASIC and APRA.
"This is a practical inquiry by APRA, it isn't a show trial, it isn't a political witchhunt, it isn't any sort of political process. They are an independent regulator. The things that a Royal Commission could potentially recommend, we're already doing it."
David Ellis is an analyst with financial specialists Morningstar.
He says investigations into CBA shouldn't be politicised.
"It's important for all stakeholders - so that's customers and staff and shareholders - that the inquiry is independent and is transparent and without any political interference. Without any political interference."
In a statement CBA Chairman Catherine Livingstone acknowledged the community's trust in the bank had been weakened.
She welcomed the inquiry and said APRA's oversight would ensure transparency.
A final report from APRA will be made public and is expected six months after the inquiry officially gets underway.
