The Advertising Standards Authority has rejected National's appeal over its misleading 'car tax' advert.
The ads, which ran on Facebook and Twitter, targetted the Government's low-emissions car feebate scheme.
They asked viewers: "What hope does an ordinary Kiwi have for getting some relief from taxes and costs if the people running the government think $6000 is a small fee?"
It was accompanied by the phrase "Labour's car tax" but showed a picture of Green Party MP Julie Anne Genter.
The Advertising Standards Authority (ASA) had said the ads, which accuse the Government of implementing a $6000 "car tax", were "likely to confuse or deceive consumers".
The ASA board looked at the evidence, and concluded the $6000 fee would only apply to a minority of vehicles, and the cost would be borne by the supplier - not the consumer. It ordered the ads taken down.
However National appealed the ruling, arguing that the Complaints Board had not given sufficient weight to the Government’s car tax policy in its totality.
It said it was clear that the costs of the policies will be passed on to consumers, in the form of higher vehicle prices.
However the ASA Appeal Board rejected this.
"The Appeal Board said the advertisement was misleading because it made a blanket factual statement, without any qualifications. The substantiation provided by the Advertiser did not support the likely consumer takeout of the advertisement," the ASA Appeal Board said in a statement.
"Therefore, the Complaints Board decision that the advertisement was in breach of the Advertising Standards Code stands."
The ASA has requested the Facebook advertisement be removed within 24 hours and then the ASA advised that this has been done.
Asked for comment following the ruling, National leader Simon Bridges didn't agree National mislead the public.
"At the end of the day, we thought we were right. We respect their decision. The ad's going to be taken down," he said. "I'm not about to get into a dispute with the ASA."