Two Australian lawyers have been barred from entering Papua New Guinea, after preparing to represent authorities in a case against PNG Prime Minister Peter O'Neill, who has been served an arrest warrant for alleged official corruption. 
Queensland barrister Greg Egan and his junior counsel Terence Lambert, argue their travel ban is "a ploy" to further undermine the case against Mr O'Neill.
Australia's Department of Foreign Affairs and Trade has declined to intervene.
A letter signed by PNG's Chief Migration Officer Mataio Rabura on   September 8, seen by Fairfax Media, instructs international airlines not to carry the men.
Last year, investigators served an arrest warrant on Mr O'Neill, after an investigation by police and anti-corruption agency Taskforce Sweep. Mr O'Neill responded by sacking the country's Attorney-General.
Mr Egan, who has been practising law in PNG since 1988, and Mr Lambert, last week lodged papers with the PNG National Court of Justice for a judicial review of the case.
"The imposition of this ban on lawyers representing the legitimate interests of people in PNG, to my memory, is unprecedented," Mr Egan said.
"The people of PNG need support on many fronts. The last thing they need is a breakdown of the rule of law."
PNG's Law Society president Peter Kuman said in a statement the lawyers held valid practising certificates allowing them to operate in the country. "All lawyers in this country must be able to practise law in this country without fear or favour."
A spokesman for Mr O'Neill would not comment.