The MP for Madang says Papua New Guinea's government led by Peter O'Neill is illegitimate and any executive decisions it makes will be liable to be illegal and unenforceable in law.
Sir Arnold Amet, who is a former chief justice, was the attorney general until Mr O'Neill and his supporters ousted the administration of Sir Michael Somare last August in a move still being contested in court.
Sir Arnold has called on public service agencies not to be coerced, intimidated or threatened to making any rash decisions that will be rendered null and void.
He says last week's sudden deportation of a New Zealand businessman and Port Moresby resident, Graham Osborne, was a despotic, dictatorial and vindictive action.
More importantly, he says there are natural justice procedures to enable residents to be heard in their defence against any allegations levelled against them, before decisions are made to deport.