The Vanuatu opposition leader, Edward Natapei, says the Speaker has contravened the standing orders of parliament by not allowing an immediate vote for prime minister, following this afternoon's resignation of Sato Kilman.
Mr Kilman, who was facing a vote of no confidence, resigned before any vote could be held.
The Speaker then adjourned the sitting and announced an extra-ordinary session on Thursday next week when the election of a new prime minister would be held.
Mr Kilman is leading a caretaker administration until then.
Mr Natapei says the adjournment is a delaying tactic and the opposition is seeking a court order to have parliament reconvene earlier.
"We suspect that they want to buy time so that they can start negotiating again, hopefully to try and get some of the members who are currently with us to cross the floor and build up their numbers so they can elect one of their members to become the prime minister. Unfortunately it is going to be a very difficult task for them."