A French Polynesian nuclear test veterans group has raised its concern that contaminated gravel is about to be used for road construction on Mangareva.
The Association 193 said huge quantities of gravel are about to be shipped from Hao atoll which was one of the military bases used in the era of the nuclear weapons tests.
The group said the gravel is contaminated with plutonium.
An Association member from Mangareva has told the public broadcaster that his group will block the ship once it arrives in the port of Rikitea.
The public works ministry said the gravel is not contaminated but made up of broken down concrete structures.
Hao was a key base until 1996 when France stopped its nuclear weapons tests.
The atoll is seeking an economic revival with the construction of large fish farms to supply the Chinese market.