The High Court will rule today whether the government was legally allowed to detain a group of 157 asylum seekers at sea for almost a month.
If it was not legal, their lawyers will seek damages.
That follows a legal challenge mounted on behalf of a Christian Tamil Sri Lankan named only as CPCF.
The boat on which he and family members were travelling was intercepted 16 nautical miles off Christmas Island on June 29, 16 days after departing India.
This was the only asylum seeker boat to reach Australia last year.
At first, the government decided to return them to India, but by July 23 that option was deemed no longer practical.
Four days later, they arrived on Cocos Island and were transferred briefly to the mainland before going to Nauru.
The group spent almost a month detained on the customs vessel Ocean Protector.
Human Rights Law Centre director Hugh de Kretser says their treatment was cruel and in clear breach of international law.
This case will decide whether it was in breach of Australian law as well, he said in a statement.