The Kiribati High Court has ruled that the speaker of Parliament must allow the opposition to move a motion of no confidence against the president, as the government tries to fend off a challenge linked to its support of China.
The speaker, Tebuai Uaai, blocked two motions by Ioteaba Tebau on 31 October.
Mr Tebau is part of an opposition bloc which now holds a majority in Parliament for the first time in three years.
On Monday, the High Court upheld Mr Tebau's complaint, ruling that the speaker's move was "erroneous and insupportable."
"The plaintiff's application must succeed," the judgement said, in reference to Mr Tebau's motion of no confidence.
It is unclear whether Mr Uaai will honour the High Court judgement.
The leader of the Kiribati Moa, or Kiribati First, Party, Banuera Berina said the opposition - which has 26 of 45 occupied seats in Parliament - was already making arrangements for a motion to hold a vote on Wednesday or Friday.
The opposition has been bolstered by discontent over the government's recent opening of diplomatic relations with China after it ditched Taiwan. The justice minister, Natan Teewe, resigned last week.
Mr Berina has said that, if elected, his party would review ties with China, which he accused of leaving Pacific nations debt-straddled.
President Taneti Maamau has described the opposition, who used a recent boost of government defectors last week to defeat three government bills, as "traitors".