The three directors of the $92 billion Cbus super fund appointed by the CFMEU have quit or been forced out under pressure from the administrator now running the disgraced union.

That followed questions from Australian Prudential Regulation Authority on whether a total of seven union-appointed directors at Cbus and two other building industry funds were fit to hold the role. But who replaces them, and how, should be part of a wider discussion about boards in Australia.