The president of New Caledonia's Congress has removed the Kanak flag from the reception area of the presidency and changed the building's exterior lighting to show the French colours.
The decision was made by the Congress president Gael Yanno who explained his move as being consistent with the undertaking of having both the French and the Kanak flag flying outside the building.
His predecessor Thierry Santa, who is also a veteran anti-independence politician, has told local media that Mr Yanno should have shown neutrality.
A pro-independence politician Louis Mapou says the change is unacceptable, given the importance of symbols.
In a month, voters will go to the polls to decide whether New Caledonia should become independent.
Since 2010, both the French and Kanak flags have been jointly used on key public buildings.
However, in 2011 four governments collapsed amid a row over the flags.