In Fishwick v. Cleland, one of the contentions put by counsel for the plaintiff was that the Papua and New Guinea Act 1949-1957 was invalid as inconsistent with the Charter of the United Nations and the Trusteeship Agreement—
The power of the Commonwealth to pass [the Act] depends either upon s. 51 (xxix) of the Constitution or upon s. 122.3 Section 51 (xxix) does not grant power to pass legislation inconsistent with or contrary to a validly existing treaty.... Even if s. 122 does apply, the powers granted by that section are limited by the purposes and prohibitions of the Trusteeship Agreement in the same way as those granted by s. 51 (xxix).... [I]f the Commonwealth relies upon the external affairs power, and relies upon a treaty as feeding that power, it must confine itself, broadly, to carrying the treaty into effect.