The French prime minister has decided that the Kanak flag can only be flown at New Caledonia's polling stations during next month's independence referendum if there is also a French flag.
In instructions to New Caledonia's 33 mayors, Edouard Philippe also said the presence of a flag other than the French one should not be considered as a political endorsement that calls into question the sincerity of the vote.
Mr Philippe's makes no direct reference to the Kanak flag, calling it instead the "second flag".
For almost a decade on most public buildings both the French flag and the flag of the pro-independece FLNKS are flown.
The Noumea Accord calls for New Caledonia to adopt a new flag, but no mutually agreed design has been found yet.
Mr Philippe has also reminded officials at polling stations that they should not wear party colours as it could affect the vote outcome.
On 4 November, voters will be asked whether they want New Caledonia to become independent.