New Caledonia's pro-independence parties say they fear a victory by Marine Le Pen in the presidential election could delay or even scuttle next year's referendum on independence from France.
Two of the parties making up the FLNKS umbrella group are calling for a vote against her and to choose Emmanuel Macron.
They say her winning the presidency could also radicalise New Caledonia's right which is split over whether to proceed with the plebiscite.
Under the Noumea Accord, a referendum has to be held by November next year.
The French government has said it will go ahead and no presidential candidate has suggested the process should be altered or abandoned.
Last year, Ms Len Pen's party said she would respect the planned referendum if she won the French presidency.
In the run-up to last weekend's first round of the presidential election, the two FLNKS member parties urged to vote for the Socialist candidate Benoit Hamon.
The Caledonian Union, which is the main FLNKS party, has issued no advice.