The High Court has allowed a demurrer and dismissed proceedings in relation to a challenge to the constitutional validity of ss 189 and 196 of the Migration Act 1958 (Cth). The plaintiffs, Iranian asylum seekers detained on Nauru since 2014, were brough to Australia under s 198B for the ‘temporary purpose’ of medical treatment on mainland Australia. While in Australia, they contended that there was no lawful basis for their detention while temporarily in Australia, arguing that a non-citizen brought to Australia for a temporary purpose cannot be detained under ss 189 and 196, because that detention would constitute an invalid exercise of federal judicial power by the Executive.

The High Court unanimously rejected that submission, allowing the demurrer and dismissing the proceeding. After reviewing the transitory and temporary purpose provisions (see [8]–[18]) the joint judges (Kiefel CJ, Bell, Keane, Nettle, Gordon and Edelman JJ) emphasised that the combination of s 198(1A) and 198AD(2) meant that a transitory person brought to Australia for a temporary purpose must be removed from Australia as soon as is reasonably practicable after the person no longer needs to be in Australia for the purpose (whether it has been achieved or not): at [18]. Throughout this time immigration detention must continue until removal at [20]. Turning to the validity question, the joint judges reiterated the principles in Chu Kheng Lim v Minister for Immigration [1992] HCA 64 — that laws permitting executive detention of non-citizens will not contravene Ch III of the Constitution if, and only if, that detention is limited to what is reasonably capable of being seen as necessary for the purposes of deportation or to enable an application for an entry permit to be made and considered — required a two part consideration: first, identifying the purpose of the detention, and secondly, considering the time necessarily involved  in the particular case to deport the non-citizen or process an application to remain in Australia (at [21]). The plaintiffs here contended that the process was invalid under each of these considerations, and the joint judges rejected both contentions.

The first contention, that their detention was not for any of three recognised permissible purposes (removal; the processing of an application; determining whether to permit an application), but rather the temporary purpose of medical treatment, was rejected by the joint judges because the temporary purpose for being in Australia is not the same as the purpose for which the person is detained: ‘The purpose of detention is not for medical treatment. Detention might even be antithetical to the medical treatment for which the person is brought to Australia.’ (at [22]–[25]). Here, the purpose of the plaintiffs’ detention in Australia ‘are the same purposes, and governed by some of the same provisions’ as all other instances involving the detention of unlawful non-citizens under s 189, namely their subsequent removal from Australia after they no longer need to be in Australia for medical treatment, or if they make a request to the Minister to be removed: at [27].

The joint judges also rejected the plaintiffs’ second contention that the duration of detention (that is, a period until the person ‘no longer needs to be in Australia’) was invalid because it was incapable of being objectively determined by a court from time to time, and because that temporal limit was not connected with limited permissible purposes of detention such that the detention power is unconstrained (at [29]–[30]). Their Honours stated that the objective determination argument misunderstood that requirement, which goes to objectively determinable criteria and precludes laws that use criteria that are so vague as to be incapable of being objectively determined: here, the duration can be determined because the preconditions for the detention and its conclusion are clear, namely that the person no longer needs to be in Australia (see at [31]–[32]). On the temporal limit point, the joint judges noted this was also based on a misconception: it was based on the assumption, rejected by their Honours earlier, that the purpose of detention was medical treatment; again the detention was for the purpose of removal from Australia when the temporary purpose no longer existed, and the fact that that was beyond the control of the Executive did not make it unconnected with a permissible purpose (at [33]).

Gageler J also allowed the demurrer and dismissed the proceedings, and made additional comments on the arguments and interpretation of ss 198(1A), 198AH(1A) and 198AD. Gageler J emphasised that the question of whether a person needs to remain in Australia for temporary purposes did not depend on the opinion, satisfaction or belief of any officer: contrary to the submissions of the Commonwealth, the question of triggering that need to remove is ‘separate from, and anterior to’ the question of the requirements imposed on officers in exercising the duty to remove: at [38], and see [39]–[41]. Instead, it is an objective question which, if a dispute arises, must be determined by a court: at [42]. When construed in this way, the statutory scheme clearly meets the objections raised by the plaintiffs in favour of invalidity: first, the detention is limited to a period needed to effectuate a purpose under the Act, and expires once that temporary purpose no longer exists (at [43]–[44]), and secondly can be objectively determined by a court, namely by examining whether the temporary purpose still exists (at [45]).