The National Party has accused the Government of spending half a billion dollars more than Treasury advised it to on climate change projects.
Meanwhile, the ACT Party said the planned cash-for-clunkers scheme doesn't justify the $500 million price tag.
But the Government said its spending is necessary to meet its climate targets.
Scientists have been telling lawmakers for decades to reduce emissions to protect both the economy and environment - but politicians can't agree on how to do so.
"Instead of taking Treasury's advice to reduce pressure on inflation, he went ahead with $2.9 billion of spending on climate change projects," said National's finance spokesperson Nicola Willis.
"This Government takes very seriously our obligations to reduce emissions and meet the goals of the Zero Carbon Act. I'm sorry the member doesn't share that," said Finance Minister Grant Robertson.
Willis is accusing the Government of blowing cash on what she said are low-value climate change projects, like helping dairy and meat processing plants transition away from coal boilers.
"So what we have here is a situation where taxpayers are funding corporates to do climate change projects that would have gone ahead anyway," she said.
But Climate Change Minister James Shaw said Willis was working on the basis of "very conservative" Treasury advice.
"The intention here is to try and get as much movement on climate action as we can," he said.
The Government also plans to help lower and middle-income families into cleaner cars, which ACT's Simon Court labelled "a cash for clunkers boondoggle".
Starting with a trial of 2500 vehicles, these will be scrapped in return for cash towards an electric or hybrid vehicle. It'll cost $569 million over four years.
Over the first two years, it'll cut emissions by 500 tonnes of CO2 if 10 percent of eligible people take up the scheme, or up to 4500 tonnes if all eligible people take it up.
For context, a typical passenger vehicle emits about 4.6 tonnes of CO2 a year.
ACT said it's not worth the price tag.
"They've admitted it won't do anything to reduce emissions and now they're calling it a social equity policy," Court said.
Transport Minister Michael Wood disagreed.
"They are modern-day climate deniers."
ACT and the National Party are of the view that polluters should pay through the emissions trading scheme and that's enough. On the other hand, Labour thinks they need to go further, but it's clear emissions savings don't come cheap - the question is whether it's money well spent.
