The leader of French Polynesia's opposition No Oe e te Nunaa party says she has no option but to vote with all other opposition forces to prevent a return of the administration of Gaston Flosse.
Nicole Bouteau's party won a single seat in last week's election of a new parliament in which Mr Flosse's Tahoeraa Huiraatira party fell one seat short of majority.
She says she would have liked to have stay neutral and maintain her party's autonomy within the assembly.
But Ms Bouteau says if she abstained in next week's presidential vote, under French law Mr Flosse would win because he is older than the opposition candidate, Oscar Temaru.
Mr Flosse says he may seek to have last week's election declared void because of voting and campaign irregularities.