Vanuatu's opposition has deposited a constitutional application, challenging the speaker of parliament's decision to reject an opposition motion of no confidence.
Philip Boedoro claimed that the opposition had forged the signatures of three government MPs.
He also said the newly elected member of parliament for Tanna, Pascal Iauko, was not allowed to sign the motion because he hadn't been sworn in yet.
Mr Boedoro also said the former speaker and the MP of Santo, Georges Wells, should not have signed the motion because he has been suspended.
But the opposition leader, Ham Lini, says the reasons given by the speaker are politically motivated.
He says the decision to declare the motion had not been in order had come from the government.
Mr Lini says the opposition wants Mr Carcasses out of his position as prime minister because his leadership could cause Vanuatu to lose its sovereignty.