The Australia Institute claims the pension fund's investment in Ferrovial is at odds with its commitment to high ethical standards and is not widely known in Norway.

It is mounting a social media campaign in Australia and Norway to convince investors to sign an open letter imploring the pension fund, known as Oljefondet, to divest.

The campaign is proceeding despite the deal to resettle refugees from the two centres because the Nauru contract runs to October next year and the government plans to keep the centre open for decades.

"Fewer detainees is better, but this is a matter of principle, not quantity, and a breach of international agreements counts whether it's 100 or 1000 people," said the Australia Institute's business and human rights adviser, Brynn O'Brien.

"The government will continue to outsource these operations, and so a divestment from Norway's sovereign wealth fund would send a strong message to the current contractor and any future bidders, that these contracts will lead to heavy public and investor scrutiny," Ms O'Brien told Fairfax Media.

"The reputation of the Norwegian sovereign wealth fund investing ethically would be tarnished by ongoing investment in these camps, in light of the incontestable evidence of abuse."

The letter says the investment clearly fails to met the ethical standards set out in Oljefondet's policy documents. "Oljefondet – on behalf of the Norwegian people – is invested in Australia's system of offshore refugee detention camps and prolonged detention, which UNHCR has described as 'immensely harmful'," it says.

"If you want Norway's money out of offshore detention, please sign the petition asking Oljefondet to divest."

A research paper prepared by the institute says Ferrovial had no association with the camps until it bought Australian company Broadspectrum in May 2016.

"At this time, Broadspectrum was operating the camps. In taking over Broadspectrum, Ferrovial acquired responsibility for the detention contracts with the Australian government," it says.

"Ferrovial made this acquisition subsequent to being provided with detailed information about the abuses in the camps. When acquiring Broadspectrum, Ferrovial fell short of conducting adequate due diligence on this acquisition, or failed to respond appropriately to human rights concerns."

The paper says that when the takeover of Broadspectrum proceeded, Ferrovial released a statement indicating that detention centre work "will not form part of its services offering in the future".

"This was widely interpreted to mean that the company would not bid for a new contract after the current contract expires, and that its work at the offshore centres would cease in February 2017 with the expiration of that contract.

"In August 2016, however, Ferrovial announced that the Australian government had extended the contract for a further eight months to 27 October 2017 (under an extension clause in the contract), despite Ferrovial's 'eagerness to withdraw' from operations at the camps."

Ms O'Brien says the paper was being sent to Ferrovial with a warning that ongoing concerns about human rights made it inappropriate for the company to contract for the services.

A spokesman for the pension fund told Fairfax Media it was aware of the issue, saying the fund was not invested in Broadspectrum at the end of 2015, and had informed its council of ethics and its investment in Ferrovial after the company bought Broadspectrum.

"We expect companies to respect human rights and address human rights issues in their business practices," the spokesman said.

A senior adviser with the pension fund's council of ethics, Pia Goyer, said the council did not comment on specific companies until it had made and published a recommendation about a company.

"Generally, when the council considers a case, first it gathers all publicly available information. At an early stage the council also contacts the company with questions and often also has meetings with companies under assessment," she said.

"The aim of the council is to assess the future risk of violations of the fund's guidelines. The preparatory works of the guidelines establish a high threshold for exclusion from the fund. Exclusion should not be used to punish a company for past violations but to prevent the fund for contributing to future violations."