New Zealand is being "cowardly" by refusing to join an international push to protect a third of marine areas, Forest and Bird says.
But the government is standing by its conservation record.
The World Conservation Congress held in Hawaii overwhelmingly passed a motion urging governments to set aside 30 percent of marine environments as protected areas by 2030.
New Zealand abstained from the vote.
Forest and Bird delegate Karen Baird said the move was shocking and out of step with the rest of the world.
The government was cowardly for not wanting to support an essential move to protect biodiversity and the planet, she said.
Conservation Minister Maggie Barry said the proposal went beyond where the government was prepared to go.
New Zealand had a strong track record for marine protection, and was currently considering other legislation, including the creation of the Kermadec-Rangitāhua Ocean Sanctuary, Ms Barry said.
Last month Prime Minister John Key conceded the government should have consulted more with fishing companies before going ahead with the Kermadec sanctuary.