The Australian Lawyers Alliance says it is concerned the Australian government has not yet made a comment on what appears to be three of its contractors illegally leaving Papua New Guinea.
Three security guards working for Transfield Services, contracted by the Australian government to run the Manus Island asylum seeker detention centre, have been accused of sexual assault of a female worker at the centre.
The PNG police say the guards were flown out of the country before before an inquiry was completed.
A spokesperson for the Australian Lawyers Alliance, Greg Barns, says it is a serious allegation and Australia's immigration department needs to speak up.
"We're very concerned as to whether or not the Australian government had any knowledge that they were leaving the island and what steps the government will take to ensure that these men return. It ought to have already made sure that those men return to the jurisdiction so they can be questioned by PNG police and it's disturbing that the Australian government has said nothing about the matter."
Mr Barns says it is clear that despite what the Australian government says, it has control over the centre and doesn't have regard to PNG sensitivities.
He said that if Australian government officials were involved in removing the guards from a potential criminal investigation then they may be criminally liable for obstructing an investigation.
Radio New Zealand International has asked the Australian immigration department for comment.