The Club Physical ad campaign, which features aliens with a penchant for body-shaming and abducting the corpulent, has sparked a series of complaints over the years.
"Get the fat ones first," said the alien characters in ads on billboards, Facebook and the firm's website.
The latest ad, for a 13-day gym promotion, implied fat humans would be the first choice for invading aliens keen on kidnapping people.
Club Physical used a picture of real people in a fun run, edited with flying saucers and nefarious-looking beams.
To "avoid being chosen", people were advised to join the gym.
The campaign has a colourful history, and has even been cited in a court dispute involving a breakaway gym franchise.
Now, the Advertising Standards Authority (ASA) has upheld multiple complaints about the latest ad.
The ad alienated multiple complainants, who called it humiliating, hurtful and offensive.
Club Physical responded that "currently Martians don't exist" so the ads were clearly science fiction, intended to be funny. The firm even compared the ads to Government-run campaigns using shock tactics to deter drink-driving.
The company said a similar aliens-and-fatties promotion a few years ago generated mostly positive feedback.
But one complainant said the latest ad used "vile tactics" and "shaming and bullying techniques" to generate shock.
They said it was specious for the firm to compare its ad to shock tactics targeting drunk drivers.
"I also hate that it's a photo taken from a fun run where the community is just trying to enjoy themselves," one complainant said.
"It's teasing and bullying on a large scale and it's not appropriate," said another.
"This advertisement is a disgusting exercise in body-shaming and uses an image of real people that likely would be embarrassed and upset to see their pictures used in this kind of awful advertisement," said yet another complainant.
The ASA's complaints board upheld the complaints, saying the ad was "likely to cause offence to most people as it ridiculed people who were overweigh".
Club Physical said it was sorry for any offence caused -- but inactivity was deadly and needed to be addressed urgently.
"Club Physical's ad was designed to encourage people to exercise with the use of humour," the company said. "Boring advertisements elicit no response."
The firm said proceeds from the $13 "fat ones" trial membership supported charity, and it would donate $1000 to KidsCan thanks to the promotion.
Facebook told the authority it investigated the ad, which had not breached the social media site's terms.
Club Physical said a Facebook header was removed anyway, on receipt of the first complaint letter.
"All other references have now been removed," the company told the authority.
However, a Club Physical video on YouTube with flying saucers above downtown Auckland and an alien declaring "Quick, get the fat ones first" was still online today. It has only attracted 122 views in four years.
Two years ago, the company's "fattist" ads were cited in court as a reason a businessman broke three franchise agreements with Club Physical.
In 2013, the New Zealand Herald reported Stuart Holder, who owned three Club Physical franchises, suddenly rebranded the clubs as Jolt Fitness.
A court heard Mr Holder was displeased about the ad showing aliens shooting fat people.
The impasse even sparked a protest, with gym-goers gathering to wave placards such as "protect franchise law".
After a High Court battle, an agreement was reached for Club Physical owner Paul Richards to take over the leases and reinstate the gyms as Club Physical.
Mr Richards did not immediately return a message last night seeking his comment on the Authority findings.
- John Weekes of NZME. News Service
