Ride me all day for ?3
The New Adventure Travel advert depicts a semi-naked woman on the back of buses holding a billboard which reads: ?Ride me all day for ?3?.
The company said it had been trying to ?make catching the bus attractive to the younger generation.?
It has attracted an angry response on social media ? including criticism by MPs.
On Facebook, one person wrote: ?Absolutely dreadful advert, what is wrong with you?!?
Another said: ?Do they seriously think they can get away with this? Women should take a stand on this and boycott that bus company.?
The advertising, which also included an image of a semi-naked man, was to mark the launch of 10 new buses on the X1 cross-city route in Cardiff, between Pontprennau and Culverhouse Cross via the city centre.
The Advertising Standards Authority (ASA) said it has received 45 complaints.
A spokeswoman said the ASA understands the adverts will be taken down within 24 hours and it will monitor the situation in case further action is needed.