Prime Minister Tony Abbott is refusing to say where a group of 153 asylum seekers are being held by Australian authorities, or whether they will be returned to Sri Lanka.
In the High Court on Tuesday the government promised to give three days notice before trying to return the group.
During the hearing the government for the first time confirmed their existence, after a week of speculation about their fate.
The group, which includes children as young as two, was intercepted at sea en route to Australia but won't be processed under the Migration Act because they never entered territorial waters.
The asylum seekers are being held aboard a Customs vessel outside Australian territorial waters, but on Wednesday Mr Abbott refused to confirm their exact location.
"I won't talk about on-the-water operations. That's to give aid and comfort to people smugglers. That's not something that I'm going to do," he told the Nine Network.
He also would not say the asylum seekers won't be returned to Sri Lanka.
"I will confirm today, as we always will, that we will operate in accordance with our legal obligation, and we will operate in accordance with safety at sea," he said.
George Newhouse from Shine Lawyers launched the court challenge, representing 48 Tamils on board the Customs vessel.
The action was sparked by the transfer to Sri Lankan authorities of a group of 41 asylum seekers on Monday, who were subject to a controversial "enhanced screening process" at sea.
Labor's Richard Marles said the opposition also took issue with the onboard screening process.
"We don't understand how you can assess people's individual cases when everyone is steaming towards Sri Lanka," he told ABC radio.
Former Prime Minister John Howard defended the Abbott government's border protection policies when asked about the 153 asylum seekers.
The standoff over the Sri Lankans has been compared by the Greens to the 2001 Tampa controversy, when the Howard government refused to accept more than 400 asylum seekers rescued by a Norwegian freighter.
"This government fulfilled to the letter the commitment it made to the Australian people in the area of asylum seeker policy and protecting our borders," he told ABC radio.
Liberal Democrat senator David Leyonhjelm is worried about the asylum seekers' fate.
"It's a bit sad, they're between the devil and the deep blue sea," he told reporters.
Independent senator Nick Xenophon trusts the High Court to make a fair decision.
Labor senator Sam Dastyari called for compassion and transparency.
"The Australian public should be able to rely on their government to tell them what's happening. We shouldn't have to solely rely on the judicial system to find out what's going on," he told reporters.
