Anti-mining protestors are accusing the Prime Minister of trying to influence the resource consent process after he officiated at the opening of the Bathurst Resources office in Wellington.
The company is applying to the Environment Court and the Department of Conservation for consents to mine 6.1 million tonnes of coal from the West Coast's Denniston Plateau.
Hundreds of protestors greeted John Key at the opening of the mining firm's office on Wednesday night.
Forest and Bird says as Bathurst has not yet received mining consents, Mr Key's appearance was a clear signal he wants those applications approved.
The Green Party's mining spokesperson, Catherine Delahunty, says Mr Key's presence sent a message that his allegiances lie with the Australian mining company.
Ms Delahunty says coal is a fossil fuel which is causing havoc on the planet.
Mr Key's office did not return calls from Radio New Zealand about the protest.