Papua New Guinea's opposition says the Prime Minister should stand aside to let the Ombudsman Commission complete an investigation into his annual statements.
Sir Michael Somare's lawyers have applied to the court to quash the investigation into his alleged failure to properly lodge a series of personal financial returns since 1992.
The deputy leader of the opposition, Bart Philemon, says the Prime Minister's failure to comply with the rules breaches the leadership code.
Mr Philemon has dismissed Sir Michael's excuse that some annual statements weren't filed because he was moving house at the time.
"That doesn't negate us from our core responsibility of making sure that our responsibilities are transparent, that we comply with the law, that we don't try to cover up in any way that will question our integrity as well as bringing the offices that we hold into disrepute."
The opposition has also called on Sir Michael to tell the truth about his government's connections to the Taiwan diplomatic cash scandal in which $US30 million earmarked by Taipei for aid to PNG went missing.