Two of the Government's support parties have refused to back proposals to overhaul planning laws.



The Maori Party and UnitedFuture say a revamp of the Resource Management Act goes too far and no longer protects the environment.



The changes were announced by Environment Minister Amy Adams last month at the National Party's annual conference. The Government wants to cut the cost of building and argues the present consenting processes take too long and are costly, slowing developments.



Adams wants to shake up part two of the RMA, which puts in place environmental safeguards.



Without the minor party support, the Government no longer has the numbers to pass the legislation.



Maori party co-leader Tariana Turia and UnitedFuture leader Peter Dunne wrote to Adams to outline their concerns.



"The changes do far more than rebalance the Act to make consenting procedures more efficient," they said in a joint statement.



"We say the changes to remove emphasis on the 'maintenance and enhancement of the quality of the environment' fundamentally rewrite the Act and put a spanner in the works of the legal system, that will take years of litigation to fix up."



Turia said the RMA was designed to ensure the use of natural resources was sustainable, and the changes undermine its purpose.



Dunne said commercial interests should not override environmental principles.



Conservationists, including the Environmental Defence Society and Fish and Game, have pilloried the Government for attacking the core principles of the 20-year-old legislation, and trading green values for economic development.



Former Prime Minister Geoffrey Palmer, one of the architects of the original legislation, has also opposed the changes.



But the Government wants to speed up building development to bring down house prices. Adams said last month that the reforms were necessary to allow councils to act decisively in giving consent.



She cited a Statistics New Zealand survey that revealed $800 million worth of projects had stalled over two years because applicants found the RMA procedures too frustrating.



The Government also claims changes to part two of the RMA only give greater recognition to the rights of property owners to use their land. Section five, which sets out the purpose and the intent of the RMA, remains untouched.



Adams was not immediately available for comment this morning. She had intended to introduce a bill to Parliament later this year. It is the third stage of RMA reforms, which National began in 2009.