The Prime Minister says National MP Nikki Kaye is entitled to make her views known about mining on Great Barrier Island.
Ms Kaye, the MP for Auckland Central, has spoken out against her party's plans for mining parts of New Zealand's most protected conservation estate.
The Government has released a discussion document outlining plans to open up 7058 hectares of conservation land for mining.
The proposals target land on parts of the Coromandel Peninsula and Great Barrier Island in the North Island and the Inangahua sector of the Paparoa National Park in the South Island, representing about 0.2% of protected land.
The announcement was made on Monday after the Cabinet considered a discussion document on the extent of mineral deposits in New Zealand, in particular in areas protected under Schedule 4 of the Crown Minerals Act.
Schedule 4 bans mining from a range of high-value conservation areas including national parks, marine reserves, wildlife sanctuaries and wetlands.
People have until 5pm on 4 May to make submissions on the proposals.
Case for mining doesn't stack up - Kaye
About 700 hectares of land on the Te Ahumata Plateau on Great Barrier would be opened up for mining under the Government's proposal.
Ms Kaye says the case for mining there does not stack up, once environmental and economic factors are taken into account.
The MP says she will strongly advocate her opposition to colleagues. However, in the meantime, she is encouraging concerned constituents to make a submission.
Auckland City mayor John Banks says people will not tolerate mining on Great Barrier. He believes local tourism and fishing industries would be affected, and the local environment devastated.
Ms Kaye says she was given approval from the Office of the Prime Minister before going public with her views.
When asked whether, if it came down to it, she would vote against her party, Ms Kaye replied that it is a time for consultation and to look at what the arguments are.
"At the moment, there's no plans for legislation, but you cross that bridge when you come to it."
PM not too worried
Prime Minister John Key says he is not overly concerned about Ms Kaye's objections.
"The party's had a long history of letting its backbenchers speak out on issues specific to their electorate ... and on that basis, I knew she was going to make the comments she made.
"That's part of a discussion document - there'll be lots of views out there and they'll all be taken into consideration. In the final analysis, the Government will make a decision."
But Labour Party leader Phil Goff says the National Party's strategy is in shambles.
"Two key members of the National Party - John Banks and Nikki Kaye - have both come out adamantly against this mining proposal. John Key's in a hole - he should stop digging."
In other National electorates
Areas earmarked for mining are also in other National electorates.
National MP for West Coast-Tasman, Chris Auchinvole, is happy with plans to open up protected conservation land in his electorate.
He says Auchinvole says any opportunity for increased wealth on the West Coast has to be welcomed.
Grey District mayor Tony Kokshoorn says he believes eco-tourism and mineral mining are capable of succeeding in tandem for New Zealand's benefit.
Mr Kokshoorn says the wider economic benefits of the proposals are clear to him.
National MP for Coromandel, Sandra Goudie, did not want to make any comment on Tuesday morning.
Environmental groups are warning the Government it will have a fight on its hands if it pushes ahead with its plans.
ECO says a broad coalition of affected groups will oppose any change, while Coromandel Watchdog says the Government will face severe opposition if it moves to open up 2574 hectares for mining on the Coromandel Peninsula.
Mining plan won't change NZ - Brownlee
Energy and Resources Minister Gerry Brownlee is adamant the proposals will not damage New Zealand economically or environmentally.
Mr Brownlee told Morning Report on Tuesday he is expecting a positive debate about the issue.
The minister says New Zealand's exports have been declining for the past five years, but government expenditure keeps growing and something must be done to put more income on the ledger.
"We've had a declining economy over a number of years, well before the (financial) crisis. We've had exports declining out of New Zealand for the last five years, yet government expenditure keeps going.
"We can't grow the economy with the Government spending more by borrowing it. We have to do some things to put a bit more income onto the ledger."
More support for plan
Hauraki District Council mayor John Tregidga says his community has lived with an open-cast gold mine for more than 20 years and the benefits must be considered rationally and discussed during the submissions period.
The business community supports the Government's proposals, saying the proper development of the mineral sector will significantly lift New Zealand's standard of living.
Mining lobby group Straterra believes there are opportunities for the industry and the economy from opening up more Crown land for mining.
