Australia’s highest court is reviewing the legality of the offshore detention of asylum seekers – a key feature of the country’s tough immigration policy.
Rights groups argue that the government violated the constitution by funding offshore detention camps on Nauru and Manus Island, Papua New Guinea.
They have reported harsh conditions, violence and abuses at the camps.
However, Australia says its policy – which is supported by both main parties – has deterred human traffickers.
Anyone who tries to reach Australia by boat to claim asylum is held in offshore centres on Nauru and Manus Island. Even those who are formally recognised as refugees are not permitted to settle in Australia.
The High Court in Canberra began reviewing offshore detention on Wednesday, in a session expected to last two days.
The case has been brought on behalf of detainees from the offshore camps who were moved to Australia for medical treatment, including a pregnant Bangladeshi woman who now has a 10-month-old child.
Rights group say the government does not have the right to send the detainees back to the camps. They argue that the government violated the constitution by funding offshore detention.
The court is expected to decide if the government acted properly when it authorised the funding. Spending on large programmes normally requires the approval of parliament.
The government says its offshore detention programme was underpinned by several laws.
Earlier this week, Nauru said it would ease curfew restrictions on the Australian-owned detention centre on its territory, effectively allowing the centre’s residents to move freely around the island.
It also said it would process some 600 outstanding claims for refugee status within the next week.
Rights groups welcomed Nauru’s move, but warned that it did not address fundamental problems with Australia’s refugee policy.
Australia’s government has denied that the move was intended to pre-empt a potentially adverse decision at the court.
Last month, an Australian senate report found conditions on Nauru were not “appropriate or safe” for detainees and urged the government to remove children from the centre.
It said allegations of rape and abuse should be investigated and access given to journalists and rights workers.
Last week, ABC aired allegations by a Somali woman who said she had been raped by two men on Nauru – and that it took police on the Pacific island four hours to respond.
Australia’s new Prime Minister Malcolm Turnbull has come under pressure to shut down all offshore migrant detention centres.
But he has defended the rules – a central policy of his predecessor Tony Abbott – by saying they are tough but save lives.