Julia Marton-Lefevre, the director-general of the International Union for Conservation of Nature (IUCN), wrote to Prime Minister John Key last week to express the "serious" and "deep" concerns of her organisation.
The Government has proposed removing areas of New Zealand's conservation estate from schedule 4 of the Crown Minerals Act - a list of protected areas deemed to have special environmental accord.
A spokesman for Mr Brownlee said the minister was unable to provide a response to the IUCN letter yesterday, because Parliament was in a session of "extraordinary urgency" debating a Bill to increase the excise tax on tobacco.
World Commission on Protected Areas (WCPA) chairman Nik Lopoukhine joined Ms Marton-Lefevre as a signatory on the IUCN letter.
The pair said the Government's decision would risk New Zealand's "valued IUCN member" reputation and also its standing in the international arena.
"Removing legislative protection to allow mining in areas that are currently protected sets a very serious precedent and risks New Zealand's respected international reputation in biodiversity conservation," the pair said.
A decision to strike areas from the schedule, diminished the "immense global importance" of protected areas at a time when the international community, through the United Nations International Year of Biodiversity, looked to governments to strengthen their commitments, the letter said.
New Zealand's WCPA spokesman Bruce Jefferies, of Wanaka, said the letter was an almost unprecedented step from the IUCN.
The "apolitical" organisation, the world's oldest and largest environmental network, rarely took a direct step to involve itself with the policy of governments, he said.
