The United Nations High Commissioner for Refugees may seek to get involved in a High Court case involving 157 asylum seekers who were detained at sea in an Australian Customs vessel.
The full bench of the High Court will determine whether the federal government has the power to remove asylum seekers from Australia's contiguous zone and send them to other countries.
Ron Merkel QC, for the asylum seekers, told the court on Thursday that the UNHCR and Australia's human rights commissioner may seek to intervene in the case.
Human rights lawyer George Newhouse said some of the government's powers had never been tested.
"What's the legality of holding them prisoner? What's the legality of putting them on little red lifeboats and pushing them off and trying to send them back to a third country?" he told reporters.
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The federal government has previously said it has the authority to prevent non-citizens from entering Australia.
The asylum seekers set off from India on June 13 and their boat was intercepted in Australia's contiguous zone, off Christmas Island, on June 29.
They have since been sent to Nauru for processing.
Mr Newhouse said the case could have international repercussions about the treatment of asylum seekers.
"What Australia's doing on the high seas does affect international law and the approach of other countries," he said.
"It's likely that we will see intervention from human rights bodies both here and internationally."
Justice Kenneth Hayne set the matter down for a two-day hearing in Canberra on October 14.
