Papua New Guinea's opposition leader will this week ask the Supreme Court to determine if the Manus Island processing centre set up and operated by Australia is constitutional.
A further transfer of asylum seekers last weekend brings their total on Manus to 155.
The Prime Minister, Peter O'Neill, has told local media that the centre is within the law, and warned the opposition not to undermine PNG's standing in the region.
Our correspondent, Oseah Philemon, says the opposition's Belden Namah wants to take the matter to court.
"It's almost like the Enhanced Cooperation Programme, where the Australian police were forced to leave Papua New Guinea, because the Supreme Court declared that their involvement in the programme in PNG was illegal. It's really the court that is going to make a ruling on it, so I think he needs to really prepare his case well before he goes to court because the government certainly is not going to let this one go."
Oseah Philemon says the courts are in recess at the moment, and it isn't known if the matter will be given any urgency.