The head of New Caledonia's pro-independence Caledonian Union has accused the SLN nickel company of prolonged tax evasion.
Daniel Goa made the accusation at a weekend party meeting, where preparations were being made for provincial elections in May.
He told delegates that SLN had evaded its duties for the past 35 years with the support of local tax authorities.
SLN, which is a subsidiary of the French Eramet mining concern, is the territory's biggest private sector employer.
Mr Goa said SLN kept blackmailing New Caledonia with threats of job losses or closure of its plant.
The mining companies are there only for the money and leave nothing except pollution and a degraded environment, he said.
SLN, which has been running at a loss, is embroiled in a dispute with employees at three of its mining sites over its planned restructure.