The Australian Prudential Authority's more extreme supervisory levers are not often in use, but APRA has chosen to exercise its legislative clout in a novel manner in the last week by opening a "prudential inquiry" into Commonwealth Bank that will report by April 2018.While much has been made about this CBA probe being unprecedented, the exercise of that power is entirely consistent with the legislative remit.Those powers reside in the Banking Act 1959 with general provisions in Section 11B that define the scope of APRA's remit which is:•    the collection and analysis of information in respect of prudential matters relating to ADIs and holding companies;•    the encouragement and promotion of the carrying out by ADIs and holding companies of sound practices in relation to prudential matters; and•    the evaluation of the effectiveness and carrying out of those practices.Everything is covered when it comes to a bank and its functioning. The evaluation and carrying out of necessary practices and almost anything done by a bank will fall into this particular section. Section 61 of the Act deals with inquiries. That section provides APRA with the power to do what it is doing in the case of CBA.APRA may appoint a person to investigate and report back to the prudential regulator on issues concerning entities over which they have jurisdiction.The regulator has named John Laker, Jillian Broadbent and Graeme Samuel to this panel.The final terms of reference for the inquiry, released on Friday cater to many fundamental matters, with financial objectives and the accountability framework listed along with the core controversies.These were expressed in APRA speak as "any core organisational and cultural drivers within CBA that have contributed to these incidents" (meaning scandals) as well as group's organisational structure, governance framework, and culture.The APRA panel is no Royal Commission into banking or one bank, but its investigators are free to fossick for treasure in any part of the Commonwealth Bank business they care to look.The bank, under the law, must cooperate with an appointed investigator, providing "access to its books, accounts and documents and must give the person such information and facilities as the person requires to conduct the investigation and produce the report".APRA is also able to give directions to CBA to make sure that it keeps itself nice, though the bank has promised to behave and help.