Lawyers for 157 Sri Lankan asylum seekers have resumed their push for a High Court trial against the Federal Government and Immigration Minister Scott Morrison.

The asylum seekers were intercepted by an Australian Customs ship after leaving Pondicherry in India in June.

They were separated and kept in windowless rooms on the ship, and were let out for three hours to exercise and eat, while their case was heard in the Australian High Court.

It had been due to proceed as a trial before the full bench of the court in Canberra in early August, but the Government moved the asylum seekers to the Curtin Detention Centre in Western Australia, before moving them again to Nauru.

At the time, a delegation of lawyers had been due to travel to the detention centre to speak with their clients.

They say they were not notified of the removal to Nauru.

Mr Morrison said they were moved offshore because they had refused to speak with Indian government representatives.

The Australian Government wants the asylum seekers returned to India.

Today, the parties were back in the High Court in Melbourne to discuss a re-framing of the case, in light of the change in circumstances.

Ron Merkel QC, acting on behalf of the asylum seekers, told the court the same principles and questions of law still applied to the case.

He said cabinet's decision-making process and the lawfulness of the Federal Government's plan to send the group to India still needs to be tested by the court.

The key to the case remains whether or not the asylum seekers were unlawfully detained by the Government, in so far as the purpose of their detainment.

That includes whether the Government had the power to take the asylum seekers to a place outside Australia and if the discharging of them from Australian custody would be unlawful.

Mr Merkel referred to the 'operational secrecy' of the Government's approach and said the issue of whether or not asylum seekers were told to paddle back to India in life boats in treacherous conditions would also come into play.

"The underlying issues have not changed," Mr Merkel said.

"The principles remain the critical issue."

Case may raise untested legal issues

Justice Kenneth Hayne said he needed to deal with the question of disputed power.

"There's an open inference from the pleading that they could not lawfully be discharged from custody in the republic of India," he said.

Lawyers for the Government asked for "a little more time" to outline their revised case.

Justice Hayne said he was anxious for the parties to bring their revised cases back to the court next week.

"I observe the act is a federal act, seeking to apply beyond Australian territorial waters," he said.

"It raises issues of a kind I believe have not been a matter for determination in this country, or elsewhere."

Justice Hayne said if the matter was referred on for trial, it would likely happen in October.

The parties will return to court next week.

Group enduring harrowing treatment on Nauru: refugee advocates

The Human Rights Law Centre's director of legal advocacy, Daniel Webb, said the asylum seekers had "endured a horrific few months".

"They spent a month locked in a boat in the middle of the ocean and we really welcome the court’s recognition that there are important untested questions about whether their treatment was legal," he said.

Mr Webb said the centre had "serious concerns" about the health of its clients, including an estimated 50 children who were on board the Customs vessel.

"Now they find themselves languishing in detention on a remote Pacific Island," he said.

"Our clients are ... very uncertain about what their future holds and they've been very uncertain throughout this whole ordeal.

"The way that our clients have been treated would be harrowing for anyone. I think it's particularly harrowing for children."