Australian banks' capital requirements could yet be raised, in the last stage of the global regulatory restructure triggered by the Basel III agreements.The Big Four Australian banks last month avoided being caught by the higher capital requirements to be imposed on around 30 so-called "G-SIFIs". The G-SIFIs are the global systemically important financial institutions such as HSBC, JP Morgan and Deutsche Bank, whose failure could endanger financial systems in many countries. No Australian bank is considered large or connected enough to qualify.But the next stage of the Basel framework will involve the so-called "domestic SIFIs" or D-SIFIs, a category which clearly includes Australia's Big Four.APRA has its own rules on treatment of the major banks, including its PAIRS and SOARS framework. It had been widely assumed that these rules would be enough to meet the requirements of Basel III.Banking Day believes that some nations within the Financial Stability Board would like to impose rules for all nations on the treatment of these D-SIFIs.This one-size-fits-all approach could require APRA, in particular, to change details of its bank supervision approach.A February report by the Financial Stability Board on the Basel III framework set out that all systemically important financial institutions (SIFIs) should "have higher loss absorbency capacity to reflect the greater risks that these institutions pose to the global financial system". That "higher loss absorbency capacity" has been taken to mean higher reserves of capital relative to assets. The February report said that "initially in particular" G-SIFIs should have this higher loss absorbency capacity.But its wording also suggests that all SIFIs, including D-SIFIs, should ultimately have a higher loss absorbency capacity.Taken at its strongest, this could result in APRA being required to impose capital requirements on the Big Four over and above what the Basel III framework requires.The increased capital surcharges for G-SIFIs ranged between 1.0 and 2.5 per cent. That suggests that additional requirements for D-SIFIs could range up to one per cent.It is not yet clear how many nations within the Financial Stability Board will push for a one-size-fits-all approach. But different views on the approach to D-SIFIs have the potential to damage the broad international regulatory consensus over implementing Basel III.