New Zealand First says it will no longer support a law change to create an ocean sanctuary around the Kermadec Islands.
Groups such as the World Wildlife Fund, Forest & Bird and the Pew Charitable trust, as well as Hollywood director James Cameron have been lobbying for the sanctuary for years.
The bill establishing the sanctuary passed its first reading in Parliament unanimously last month.
Yesterday, the Labour Party and Maori Party said their support for the bill was not guaranteed.
A Maori fisheries trust has taken legal action and several prominent Maori leaders have publicly opposed the sanctuary, arguing the Government has ignored the impact it will have on iwi fishing interests.
The New Zealand First leader Winston Peters says the sanctuary breaches a 1992 Māori Fisheries Settlement and he does not support the Government breaking its word.