The Abbott government is fast-tracking the removal of asylum seekers who arrived by boat and have had their refugee claims rejected by authorities.
The Asylum Seeker Resource Centre claims it has been told of secret plans for a "mass round-up" of asylum seekers in the community for detention and possible deportation.
It also claims asylum seekers who have had their refugee applications rejected by the immigration department and Refugee Review Tribunal would be offered six-week bridging visas and "encouraged" to make arrangements to leave the country.
If they did not leave voluntarily they would be detained and face potential deportation.
The centre's chief executive Kon Karapanagiotidis told AAP an immigration detention centre in Darwin had been earmarked as a "removal centre".
The move could affect people who plan to seek judicial reviews or ministerial intervention.
Immigration Minister Scott Morrison confirmed the government was taking steps to "to remove failed asylum seekers from Australia who wish to stay indefinitely at taxpayers' expense".
"Once you have had your asylum claims assessed and rejected not just by the department but also on appeal, it's time to go home," he said in a statement on Thursday.
If people co-operated with the department it would be willing to allow them to remain in the community while they arranged departure.
"For those who do not wish to co-operate and seek to frustrate the process, then the government is left with no option but to take them back into detention," Mr Morrison said.
Where asylum seekers had sought judicial review their cases will be allowed to run their course.
Detention of people involved in ongoing cases was decided on a case-by-case basis, Mr Morrison said.
"Any suggestion that anyone is being forced to abandon their appeals is nonsense."
The government has softened its stance on the refugee appeals process.
Before the election the coalition had promised to abolish the Refugee Review Tribunal and instead task a single case officer to review failed refugee claims.
It also vowed to axe access to legal aid for appeals.