The Greens have attacked Labour's proposed emissions trading scheme, saying it amounts to a $1.2 billion subsidy for the dairy industry.
Under the scheme, agriculture would not have to participate until 2013.
Greens co-leader Russel Norman yesterday said that would see the taxpayer having to spend millions of dollars to buy carbon credits to cover agricultural emissions during that period.
"The dairy industry is going through boom times and can afford to cover the cost of their increased emissions, rather than relying on the taxpayer to pick up the bill, which would also give the industry a good reason to use available technology to reduce their emissions," Dr Norman said.
"The fact they are doing well is a tremendous thing and they should be congratulated for that ... but even so they should still pay their way. They shouldn't be subsidised by the taxpayer to the tune of $1.2 billion."
The volume of emissions and the cost of carbon credits are much debated by all sides of the climate change debate.
Simon Terry, the executive director of the Sustainability Council, has put the value to the agriculture sector of not joining the scheme until 2013 at closer to $1.56 billion.
Yesterday, Climate Change Minister David Parker disputed the Greens' figures, saying the Government estimated the cost of carbon credits at around half that claimed by Dr Norman.
Mr Parker said the agriculture sector - which is responsible for almost half of New Zealand's greenhouse gas emissions - was committed to reducing them, and was working closely with the Government to do so.
Federated Farmers president Charlie Pedersen said attacking the dairy sector had become a popular occupation for "fringe groups".
He said farmers were now at world best-practice levels for producing food, and aimed to do better.
"Fewer emissions are produced by New Zealand agricultural producers than anywhere else in the world per kilo of food produced, " Mr Pedersen said.
"They are also not recognising that agriculture is already investing millions of dollars, and has done so for three years now, into the greenhouse gas consortium to look for research tools that will enable us to reduce our emissions further."
Dr Norman said there was already technology available for farmers to reduce emissions, and the agriculture sector should be moved onto the same timetable as fuel companies to join the scheme - 2009, rather than 2013.