New Zealand's advertising watchdog has ruled against a group that used a billboard to try to claim vaccination is risky.

The billboard advertisement for Waves NZ, erected above Auckland's Southern Motorway, showed a photo of a man, with a prominent Maori-inspired tattoo on his arm, holding a baby.

Alongside the picture were the words: "If you knew the ingredients in a vaccine, would you RISK it?"

The Advertising Standards Authority (ASA) received nearly 150 complaints about the billboard, slamming the advertisement as misleading, deceptive, scaremongering and socially irresponsible, given that convincing people not to vaccinate was harmful to children and to wider society.

Complainants also criticised its placement in a low decile area as "predatory in nature" and attempted to mislead "a disadvantaged sector of society".

Another said: "To place this hoarding near a hospital is yet another despicable act of an amoral group of fraudsters."

The billboard owners told the ASA the advertisement was installed without going through their normal vetting process and if they had followed it correctly, it would not have been installed.

Once the issues with the billboard came to light, the owners removed the advertisement "as quickly as possible".

Waves NZ argued it could see no reason why the advertisement breaches the ASA's Code of Ethics, claiming its intention was to promote "informed consent" and to point parents toward MedSafe data sheets on its website.

But the majority of ASA's complaints board said the identity of the group behind the billboard wasn't sufficiently clear, and ruled the code's identification requirement hadn't been met.

A minority disagreed, saying most consumers would be able to identify that the group was anti-vaccination, taking into account the advertisement overall, and the impact of the image and the text combined.

The board found the advertisement was also misleading, as the likely message that vaccination was not safe wasn't "sufficiently substantiated" by the advertiser, its advertisement "unjustifiably played on fear", and was "socially irresponsible".

The board upheld the complaints, finding the advertisement in breach of several rules of its Code of Ethics.