National MP Judith Collins has revealed she considered "crossing the floor" over her party's backing of the Zero Carbon Bill which has passed its final reading.
Collins - who has spoken out strongly against the legislation - revealed in a Facebook post she "considered very carefully whether to 'cross the floor' on this issue".
That means she would have voted against her own party, which is considered a rare move.
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When former National MP Marilyn Waring voted with Labour to ban nuclear ship visits in 1984, then-Prime Minister Robert Muldoon called for a snap election and Labour won.
Collins said in her post she respects "collective decision-making" within National, and she's agreed to amendments the party has promised to make if elected in 2020.
National leader Simon Bridges announced those amendments on Thursday after pledging his party's support for the legislation.
It includes leaving it up to the Climate Change Commission to decide on a methane reduction target, prompted by National's opposition to the Bill's current target of 24-47 percent biogenic methane reduction by 2050.
Federated Farmers says the current target "remains eye-wateringly hard for farmers to achieve".
Prime Minister Jacinda Ardern said in her speech that the legislation already allows for the commission to make changes: "The claim that we should listen to the Climate Change Commission is already embedded in the legislation."
She said the commission would be able to give any government of the day their advice on targets and that includes the methane reduction target, based on scientific evidence.
Collins said she fought to secure the promise from National that changes will be made to the law if National's elected in 2020, which will also include more protections for farmers around food production.
"Our Bill, in amendment, will make clear the stated aim of the Paris Agreement that it's for greenhouse gas reduction but it does not threaten food production."
In her Facebook post, Collins said: "New Zealand farmers have been targeted by this government and New Zealand First voted against every amendment that we put forward.
"New Zealanders, who do not want to see our economy suffer, will need to vote us in at the next election so we can honour our commitment to them."
In her speech to Parliament, Collins described the Bill as "deeply flawed".
The Prime Minister said in her speech that New Zealand will "not be a slow follower" on dealing with climate change compared to the rest of the world.
"We will not be a slow follower, because, quite frankly, we cannot afford to be, not for the environment but nor for our food producers. They trade on our brand and our name."
Collins spoke after Ardern, telling the Prime Minister she had a "message" for her: "New Zealanders do not want to be first and fast and furious; they want to have a fair go."
"What we're seeing from the Prime Minister... is that she's very happy for New Zealand farmers to be sold down the river and for New Zealand's economy to go with it."
Ardern said she hopes the next generation "will see that we in New Zealand were on the right side of history".