More than 150 asylum seekers are being held behind locked doors on a customs ship, in rooms without windows and with no idea where they are or where the Abbott government plans to take them.
Their boat was intercepted near Christmas Island more than two weeks ago.
A document lodged with the High Court on Wednesday provides the first news of the asylum seekers, who set off for Australia from India on June 13, since the government confirmed they were being held on a customs vessel more than a week ago.
They have no freedom of movement, can only leave their rooms in the presence of guards, and do not know who the guards are, the document says.
It also reveals that their possessions, including any mobile phones, were seized when they were detained, and asserts they are being denied ''reasonable access'' to legal advice.
Lawyers representing them are now seeking a High Court order that they not be taken to Sri Lanka, Nauru or Manus Island, saying the government has no power to take them to a place, other than Australia, against their will.
The case will be the first comprehensive test of whether the government has the power to intercept boats on the high seas, hold asylum seekers against their will and take them where it chooses.
Immigration Minister Scott Morrison continued to refuse to provide any information on the boat in Parliament on Wednesday, instead accusing the opposition of being ''a field of dandelions'' when it came to border protection. ''What a bunch of jellyfish you are!'' he taunted.
The court document was filed as the United Nations refugee agency expressed alarm that Australia may have breached a cornerstone of the refugee convention by returning another group of asylum seekers to Sri Lanka after intercepting their boat at sea.
Volker Turk, the director of international protection for the United Nations High Commissioner for Refugees, said there was a serious risk that the ''enhanced screening'' of claims at sea fell well short of requirements for the fair processing of claims. It could mean that asylum seekers were returned, or refouled, to persecution.
''You can only ensure respect for the principle of non-refoulement if you have in place proper and fair procedures that identify, with due process, who is in need of international refugee protection and who is not,'' he said.
In an exclusive interview with Fairfax Media, Mr Turk also expressed concern at the fate of the 153 asylum seekers on the customs vessel, whose boat was about 27 kilometres from Christmas Island when it was intercepted on or about June 29. A High Court directions hearing on their case is set for Friday, with the case likely to begin on August 5.
According to the amended writ of summons lodged on Wednesday, all are of Tamil ethnicity and Sri Lankan nationality, with the possible exception of children born in India. The only information sought from the asylum seekers has been their names, ages and addresses, it says.
It seeks a declaration that the Commonwealth acted unlawfully and an injunction preventing them from being taken to Sri Lanka, Nauru, PNG or any other country that has not assumed international non-refoulement obligations.
Mr Turk said that while the world faced a displacement crisis that was ''probably unprecedented since the end of the Second World War'' he was ''absolutely'' concerned about the message that Australia's approach sent to the rest of the world. ''You cannot extrapolate Australia's approach to the rest of the world because, if that was the case, you would spend an enormous amount of resources on moving people from one country to the next and keeping them in limbo,'' he said.
He said the UNHCR shared Australia's concern about people smuggling and loss of life at sea, but pointed to the approach of Italy, which had rescued 64,000 asylum seekers in the Mediterranean since the start of the year.
