Billions of dollars' worth of contracts for offshore processing centres should be made public, Amnesty International says.
The push coincides with a visit from Nauruan President Baron Waqa, who will meet with Prime Minister Malcolm Turnbull as the two countries continue to wait on the United States to resettle refugees from the island.
The Department of Immigration and Border Protection (DIBP) has previously been accused of mismanaging contracts for the centres on Nauru and Manus Island in a series of independent audits.
Reports from Australian National Audit Office (ANAO) alleged more than $1 billion was spent over the last four years without proper authorisation.
In its report issued today, Amnesty International criticised the "secrecy" surrounding contracts with Broadspectrum — previously known as Transfield — and its parent company Ferrovial.
Broadspectrum is the leading private contractor for the centres and had provided garrison services on Nauru since September, 2012.
The company expanded its contract — previously worth $350 million — in 2014 to cover garrison and welfare services on Nauru and Manus Island.
Its $2.5 billion contract with the Immigration Department was originally supposed to end in October 2015, but was extended until October this year when the company will not bid to renew it.
Money made in 'stark contrast to shockingly poor conditions'
The report, titled Treasure I$land, stated that the exact profit Broadspectrum makes from its contract with the DIBP has never been disclosed.
"Ferrovial has not released details of Broadspectrum's exact profits from the DIBP contract, saying that it is confidential," it read.
"The vast amount of money that Ferrovial and Broadspectrum make from the DIBP contract stands in stark contrast to the shockingly poor conditions in which refugees and people seeking asylum have been forced to live at the RPC [regional processing centre] on Nauru since it has been operated by Broadspectrum."
Amnesty International said the cost of keeping people in offshore centres — estimated at $573,111 per person per year by the ANAO — meant taxpayers had a "legitimate interest" in the full disclosure of the contracts.
It also called on the Government to stop using offshore processing as part of its border protection policies, which have reportedly cost around $10 billion since 2013.
The Gillard Government was responsible for first transferring asylum seekers to the centres in 2012 after former Labor leader Kevin Rudd dismantled the Howard Government's Pacific Solution in 2008.
Immigration Minister Peter Dutton has previously blamed former Labor Governments for mishandling contracts for the centres before the Coalition came to power in 2013.
Further comment has been sought from the Immigration Department.