Australia's opposition Greens have spoken out against reported plans to hold asylum seekers and suspected illegal fishermen in privately owned floating prisons.
Australia is reviewing asylum laws and wants to channel processing through off-shore centres, including the ones on Nauru.
A Greens senator, Kerry Nettle, says Australia's human rights record would be brought to a new low if the latest plan was carried out.
Ms Nettle says the proposal appears to allow customs officials to detain without charge or access to legal support for a month in prison cells on board a private ship.
She says this policy harks back to Australia's penal history, when it should be at the forefront of compassionate and human solutions to border issues.