A month-long stand-off on the high seas involving the detention of 157 Sri Lankan asylum seekers on a Customs boat will be examined in the Australian High Court on Tuesday.
The case to determine the federal government's power to remove asylum seekers from Australia's contiguous zone, just outside territorial waters, and send them to other countries will come before the full bench in Canberra.
The matter centres on just one of the 157, a Tamil Sri Lankan asylum seeker.
The group set off from India on June 13 and authorities intercepted their boat 16 days later, 16 nautical miles off Christmas Island. It is the only official boat arrival to Australia this year.
The asylum seekers spent almost a month detained on the Customs vessel Ocean Protector, before being sent to the Curtin detention centre in Western Australia.
Lawyers for the Tamil asylum seeker are seeking damages for unlawful detention and will argue maritime power laws were breached.
The government tried to return the group to India but when that option fell through they were sent to Australia's Cocos (Keeling) Islands.
The asylum seekers are now in detention on Nauru.
The government's legal team will insist the detention at sea was legal and the plan to send them to India did not breach Australia's non-refoulement obligations under international law.
The United Nations High Commissioner for Refugees and the Australian Human Rights Commission are seeking leave to intervene in the case. The court's ruling could have international repercussions. (AAP)