The Supreme Court in Vanuatu is reviewing the parliamentary Speaker's dismissal of a no confidence motion in the Prime Minister, Charlot Salwai.
The motion was brought last week by the opposition, which said 30 MPs in the 52 seat house, including government MPs and cabinet ministers, had signed.
Speaker Esmon Saimon declared the motion out of order, saying the date chosen for the extra-ordinary session of parliament to hold the vote, Friday this week, clashed with the parliamentary schedule.
Mr Saimon also challenged the validity of the signatures.
The opposition took the matter to the Supreme Court today and the opposition leader, Ishmael Kalsakau, said they would return to court on Thursday to further test the Speaker's claim.
"It is settled law in Vanuatu. Article 21/2 of the Constitution does not confer upon the Speaker a discretion to make any enquiry as to whether or not members of parliament signed, or did not sign, a motion of no confidence," Mr Kalsakau said.
"That becomes the exclusive domain of parliament itself. That law has been settled by the Court of Appeal on numerous occasions."