The government in New Caledonia is planning a tax on nickel ore.
The president Harold Martin says the levy would be a strong fiscal measure, but two major operators in the country may be exempt.
The proposal provides for taxes of between 2.5 and 5.5 percent on the export value of the resource, depending on its grade and whether the ore is refined before export.
The tax could come into force at the beginning of next year and the revenue would be put aside for future generations, towards economic diversification, savings or in case of crisis.
Mr Martin says the country's two major nickel operators Swiss-listed Xstrata and the Brazilian operation in the south, Vale, are subject to agreements on fiscal stability but expert advice is being sought on the proposal.
The draft law next goes to a vote in New Caledonia's Congress.
New Caledonia has a quarter of the world's nickel reserves and it is expected to become a major global supplier of the metal in coming years.