A High Court ruling on our powers over Sri Lankan asylum seekers could decide much more than the fate of the 153 people on a boat - it could redefine the constitutional balance of our democracy, writes Joyce Chia.

Yesterday's High Court hearing on the potential return of Sri Lankan asylum seekers raises profound questions about the separation of powers and the rule of law in Australia.

The central question for the court is: does the Australian Government have the power to intercept a boat and return asylum seekers to Sri Lanka?

It is clear that returning people to Sri Lanka after inadequate screening at sea raises a real risk of refoulement (returning people to persecution or other serious harm), which would violate international law. So much was plainly stated by 53 legal scholars earlier this week. The High Court hearing raises another, more complicated, question: is this also unlawful under Australian law?

In the hearing, the Australian Government indicated it would seek to justify its actions under the Maritime Powers Act 2013. This Act, adopted last year, consolidated a range of maritime powers, including powers to board vessels, search places and people, and detain vessels or people.

The story so far 153 asylum seekers intercepted off the coast of Australia.

153 asylum seekers intercepted off the coast of Australia. A High Court hearing on Tuesday heard the group is being held on an Australian Customs vessel.

A High Court hearing on Tuesday heard the group is being held on an Australian Customs vessel. The Government may seek to return the asylum seekers to Sri Lankan authorities. It already handed over another 41 asylum seekers to the Sri Lankan navy on Sunday.

The Government may seek to return the asylum seekers to Sri Lankan authorities. It already handed over another 41 asylum seekers to the Sri Lankan navy on Sunday. Lawyers acting for about one third of the asylum seekers are seeking to challenge the legality of the Commonwealth's actions.

Lawyers acting for about one third of the asylum seekers are seeking to challenge the legality of the Commonwealth's actions. The Government has agreed not to return the asylum seekers to Sri Lanka without three days' notice.

The Government has agreed not to return the asylum seekers to Sri Lanka without three days' notice. The hearing has been adjourned until Friday morning.

The Act does not, however, appear to allow the government to "turn back the boats" or to transfer asylum seekers to another country. Indeed, Coalition Senators objected to the Act precisely because they thought it might prevent the Coalition Government from turning back boats.

If the Australian government cannot rely on the Maritime Powers Act, a larger question looms: can the executive power under the Australian Constitution be used to justify the Government's actions? This would require the High Court to revisit the famous Tampa case of 2001, where the full Federal Court found that this power allowed the government to exclude non-citizens, despite the elaborate provisions of the Migration Act.

One possibility is that the High Court may decide to overrule the Tampa judgement. The court's decision in that case was not unanimous, and has always been controversial. The more likely possibility would be for the High Court to find that there are important differences between this case and the circumstances in Tampa, which could lead to a different outcome in this case.

One important difference is the existence of the Maritime Powers Act itself, which was intended to provide a "comprehensive framework" for the exercise of maritime powers. An argument could therefore be made that this Act replaces any previous executive power.

Another important difference is that the Tampa decision only considered the power to prevent a vessel from docking at an Australian port, to restrain a person or boat from entering Australian waters, and to compel it to leave. Actions such as transferring asylum seekers to their country of origin were not considered.

Perhaps the most important difference is that the Migration Act now expressly covers the transfer of asylum seekers to regional processing countries. These provisions were introduced into the Act shortly after the full Federal Court's decision on Tampa. Although the provisions have since been diluted, the Act does include a degree of parliamentary oversight.

The key question in the present case is whether the Government has power, outside of any legislation, to transfer asylum seekers outside Australian waters to Sri Lanka. If it does have such power, this may effectively allow it to bypass both the Maritime Powers Act and the Migration Act. The existence of such a power could arguably also prevent the operation of the Migration Act.

The Government could intercept and return people before they ever engaged Australia's domestic legal obligations.

This case therefore raises profound constitutional questions about the accountability of the executive to Parliament, and the principle of the rule of law. The rule of law requires the executive to act in accordance with the laws of the land, made by the elected Parliament.

In the end, this court case could decide much more than the fate of the 153 Sri Lankans on the boat - it could redefine the constitutional balance of our democracy.

Dr Joyce Chia is the senior research associate at the Andrew & Renata Kaldor Centre for International Refugee Law. View her full profile here.