The Vanuatu opposition leader, Sato Kilman, says they have the numbers to topple the government.
The Supreme Court ruled last Thursday that parliament had to be called within seven days to consider a motion for a vote of no confidence brought earlier this month.
Since the motion was tabled, the National United Party has joined the government, and Mr Kilman says he is now not sure how the Speaker will interpret the court directive.
But Mr Kilman says if the vote goes ahead they have the numbers despite government claims that more than two thirds of the 52 MPs now support their seven-party coalition.
"We have in the Opposition at the present 26 members - now I don't know how the government can say they have 35, but we definitely have 26 confirmed members of the opposition."