The Human Rights Law Centre says the engineering firm Canstruct will be complicit in serious human rights abuses if it takes over the contract to run Australia's immigration detention centre on Nauru.
The centre said a leaked memo from Canstruct's chief executive showed the company would run the Nauru centre by the end of the month.
Nauru's previous contractor Broadspectrum pulled out after a sustained campaign by human rights groups.
The Human Rights Law Centre's Keren Adams said Canstruct should be aware of the risks of being associated with the detention centre.
"They've been written to by both Amnesty International and the No Business in Abuse campaign warning them as to what had happened to other companies that had become involved in the centres and warning them that they would be in clear breach of their international human rights obligations," Ms Adams said.
"I hope that they reconsider their decision to become involved but if they don't they're going to be opening themselves up to a world of criticism."
Canstruct International directed questions about its contract to the Australian Government, which said it would continue to provide services to detainees on Nauru.
stated Canstruct intends to rehire Broadspectrum staff currently providing garrison and welfare services on Nauru under the same terms and conditions.
It said the Queensland based company had been working on Nauru since 2012 to construct the detention centre as well as local infrastructure.