The Federal Government's controversial Border Force Act has been undermined by the extension of a Senate investigation into offshore detention facilities, The Greens say.

Greens and Labor senators voted to continue the committee that looked into the Nauru detention facility and found conditions were "not adequate, appropriate or safe".

Greens immigration spokeswoman Sarah Hanson-Young said whistleblowers who came forward would be protected by Parliamentary privilege and immune from criminal prosecution.

"The Border Force Act currently says that staff are liable for two years' jail if they speak openly, even if they see things that are wrong," Senator Hanson-Young said.

"This gets around that — if they tell the Senate Committee, if they tell this inquiry, they will be covered.

"What it does is allow for the Senate to continue to monitor what is going on there and ensure that anyone who has information that is important and is in the public interest, and they believe the Parliament and the people should know, can use this process."

The committee will allow submissions about the Australian-funded centres on Manus Island and Nauru until the current Parliament ends.

The Border Force Act passed earlier this year with Government and Labor support, along with votes from senators Glenn Lazarus, Jacqui Lambie, John Madigan and Nick Xenophon.

Committee chairman and South Australian Labor senator Alex Gallacher said the report showed serious problems on Nauru and that additional scrutiny of both offshore centres was needed.

"There clearly needs to be an avenue whereby people can express deeply felt, widely held concerns and it should be under Parliamentary privilege," Senator Gallacher said.

"We cannot have a situation where people's voice of concern is not heard."