Allegations of abuse in Nauru's immigration detention centre, including of children, are likely to come under scrutiny from the Senate when parliament returns later this month.
After more than 2000 leaked incident reports of abuse and self-harm among asylum seekers on Nauru, Labor has flagged it will move to set up a parliamentary inquiry.
It looks likely to get enough crossbench support to make this happen.
The Greens want to go a step further with a royal commission, but the federal government insists neither measure is necessary because it is satisfied with the immigration department looking into the claims.
Finance Minister Mathias Cormann said many of the claims were historical in nature and had previously been investigated.
"There are very strict processes and procedures ... to deal with any allegations of abuse and appropriate action is always taken," he told Sky News on Sunday.
Opposition Leader Bill Shorten slammed the government's approach as arrogant.
"We (need) to get to the bottom of what is really going on," he told Sky News.
Labor is yet to draw up terms of reference but expects the inquiry would look at contributing factors to the abuse, reporting mechanisms, what investigations took place, and checks and balances.
The opposition needs the votes of the nine Greens plus four crossbench senators to establish the inquiry and already looks like it will have enough support.
"I don't trust the government with this kind of stuff, all they do is shove things under the carpet," Tasmanian independent senator Jacqui Lambie told AAP, adding she was interested in participating.
Liberal Democrat senator David Leyonhjelm and the Nick Xenophon Team of three are also likely to vote in support of an inquiry.
Coalition senator Linda Reynolds cast doubt over the merits of a new inquiry, saying a previous one had descended into personal attacks and had failed to come up with evidence to back claims such as waterboarding.
Meanwhile, Labor has seized on Tony Abbott's admission he should have backed the Gillard government's 2011 people swap deal with Malaysia.
The former prime minister last week conceded that, while he doubted the Malaysia plan would have worked, backing it could have avoided some of the "hyper-partisanship" that now poisons public life.
Labor frontbencher Stephen Conroy said on Sunday if the proposal to send 800 asylum seekers to Malaysia in exchange for 4000 genuine refugees had happened there would have been no need to open the Manus Island and Nauru detention centres.
