The Commonwealth power to legislate for marriage and 'matrimonial causes' is supported by sections 51(xxi) and (xxii) of the Constitution, whereas the power to legislate for de facto financial matters largely relies on referrals by States to the Commonwealth in accordance with section 51(xxxvii) of the Australian Constitution.
However, the definitions of 'matrimonial cause' and 'de facto financial cause' differ in some respects, due to the different sources of Commonwealth power to legislate for these matters.