Lawyers acting on behalf of an Iranian asylum seeker who has been sent to Manus Island have set out the details of the case.

It is the first legal challenge to the Government's policy to send asylum seekers who arrive in Australia by boat to Papua New Guinea, which was announced a month ago.

Barrister Mark Robinson SC says his client is being held at Manus Island detention centre and his removal from Australia was invalid.

He said the man can only be identified as S156 of 2013, the High Court number given to him when proceedings commenced today.

Mr Robinson told the ABC's PM program soon after the man, who came from Iran, claimed refugee status he was sent to PNG against his will.

He said the man had a "well-founded fear of persecution because of his race, religion, or his political opinion, and believes he is a refugee in accordance with the Refugee Convention".

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Mr Robinson said the case was referred to him after the man's cousin, who has residency in Australia, sought help from lawyers.

The barrister said: "We're seeking the declaration ... that PNG is a regional processing country, we want that set aside - so, declared invalid - and we want the client returned to Australia so that he can be processed, his refugee application can be processed, in the normal course."

He said there were factors the Immigration Minister, who signed the declaration last October, had failed to take into account.

"The minister expressly said that he's not going to take into account issues relating to the domestic law of PNG or the international obligations of PNG," Mr Robinson said.

"Now, those things are plainly relevant, and it's incredible to believe that he can make a lawful decision without regard to those factors."

'No interruption to transfers' while the case is ongoing

Mr Robinson said he was unable to comment on the broader ramifications of the action.

"As I understand it, the only source of authority for Australia to be sending boat people to Manus Island and then the mainland of PNG is by reference to this declaration ... the same declaration that we are attacking," he said.

Federal Attorney-General Mark Dreyfus says the Government is confident the policy will withstand a legal challenge and it will vigorously defend the challenge.

He also said there would be "no interruption to ongoing transfers, and Australian Government policy will continue to be fully implemented while this matter proceeds".

Papua New Guinea's opposition has also relaunched a legal challenge to the immigration processing centre on Manus Island.

Opposition leader Belden Namah claims the transfer, processing and possible resettlement of asylum seekers in PNG is unconstitutional.