The former right-hand man of New Caledonia's late anti-independence leader Jacques Lafleur has warned of a possible victory of the pro-independence camp in the next election.
The Congress elected in the May election can call for a fresh independence referendum.
In an interview with the Nouvelles Caledoniennes, Pierre Bretegnier said unity among the anti-independence parties was the only way they could retain power in the provincial elections in May.
His comment comes after voters this month rejected independence from France with a margin much smaller than forecast by the polls, giving impetus to the pro-independence camp.
Mr Bretegnier said it was now imperative for the Rassemblement to side with the Caledonian Republicans and others.
He said if they don't they risk missing the threshholds to win individual seats.
The anti-independence bloc once dominated by Mr Lafleur has suffered repeated splits in recent years but jointly the newly formed parties have kept securing a majority of votes.