A Papua New Guinea opposition MP, Belden Namah, says the prime minister must say when the Manus Island asylum seeker detention centre will be shut down.
Mr Namah brought the successful Supreme Court challenge that last month ruled the Australian-run camp was illegal.
After the verdict, prime minister Peter O'Neill said the detention centre would be shut down, but the camp remains open and no plans have been announced for its shutdown.
Mr Namah said it's all very well for Mr O'Neill to say he will shut the camp, but he needs to reveal his timeline.
He said it should have already happened, but he was prepared to give the government three months.
"It should shut down already. As soon as the court decision was handed down. Immediate. It is of immediate effect," said Mr Namah.
"But three months as in, you know, in terms of demobilisation, all these things must happen. In terms of shutting down it should have happened on the day the Supreme Court handed down its decision."
Mr Namah said Mr O'Neill should resign for allowing the illegal arrangement to go ahead and vandalising the constitution in doing so.
However, Mr O'Neill said Mr Namah should stop grandstanding over the Manus Island court decision, and let the governments of PNG and Australia go about the process of winding down the centre.
Mr O'Neill said it is a significant scale of operation and the process has to be done properly in a timeframe that is acceptable to the court.
The prime minister claims Mr Namah's comments could stimulate further people trafficking and lead to the loss of more lives.