The Royal Forest & Bird Protection Society of New Zealand is considering legal action after a mining company was granted access to conservation land by Conservation Minister Nick Smith.
Dr Smith has given Bathurst Resources access to DoC land at the Denniston Plateau, near Westport, but the mine is still subject to appeals in the High Court.
A DoC report to the Minister says the mine would destroy ecosystems that are home to species found nowhere else in New Zealand.
Forest & Bird advocacy manager Kevin Hackwell said Dr Smith's actions were inconsistent with DoC's advice and the organisation is considering legal action.
He said that includes the possibility of seeking a judicial review.
The mine is still dependent on resource consent, which was granted in 2011 but is being appealed by conservationists in the High Court.