NAT Group's new back-of-the-bus promotion was seen on the X1 cross-city Cardiff service that launched this morning.
The controversial ads show a woman with bare shoulders or a bare-chested man holding a placard with the words 'Ride me all day for £3'.
But within hours of the launch, and postings on the firm's website and Facebook page, the online backlash began.
The company, which operates services through South Wales, decided to cancel the campaign within four hours after an avalanche of criticism on social media.
Anwen Kya Hayward posted: "Fire your marketing team."
Axel-Charles MN said: "This is some of the worst stuff I've seen in years.
"That is downright offensive, it would never pass the standards of the ASA. Hope you react soon."
Sally Burton said: "Reported to the ASA. What idiot ever thought this would be a good idea?"
Jessica Alfonso Robledo added: "Please remove these adverts from your buses.
"Women are not here to be objectified, we are people too.
"I couldn't use a bus with this advert on it and I would find it very difficult to explain to my four daughters why naked women are being used to sell bus tickets."
The photograph the company itself posted on its Facebook page shows only the female version but one Facebook user latest posted the male version.
Nicola McCarthy said: "Just for the record - it is absolutely NOT OK to also have a male version of this ad.
"It is NOT OK in itself and it certainly doesn't make the female version OK. Both are sexist, both are offensive."
In a statement, NAT Group said: "Firstly we have stated that our objectives have been to make catching the bus attractive to the younger generation.
"We therefore developed an internal advertising campaign featuring males and females to hold boards to promote the cost of our daily tickets.
"The slogan of ‘ride me all day for £3’ whilst being a little tongue in cheek was in no way intended to cause offence to either men or women and, if the advert has done so then we apologise unreservedly.
"There has certainly been no intention to objectify either men or women.
"Given the volume of negativity received we have decided to remove the pictures from the back of the buses within the next 24 hours."
