A south Wales bus company says it will withdraw an advertising campaign following an online backlash.
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.
The new Cardiff Central Labour MP Jo Stevens said on Twitter: "Please can you explain how your advert is in any way appropriate?"
Speaking to BBC Wales' Jason Mohammad, Ms Stevens said: "When I saw the advert, literally my jaw dropped. What on earth were they thinking on any level? This is completely crass".
Her Labour colleague in Cardiff South and Penarth, Stephen Doughty added: "Just spoke to MD @NAT_Group to express disgust at adverts - he tells me it's a 'misjudgement'."
There was also condemnation from the National Union of Students Wales, which said there was "no imaginable link between this image and bus travel".
Deputy president Ebbi Ferguson said: "There are no circumstances where this would have been appropriate.
"It beggars belief that NAT Group ever thought this was a good idea."
But following the reaction, New Adventure Travel said it would be scrapping the advertisements.
"Our objectives have been to make catching the bus attractive to the younger generation," said the bus operator.
"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.
"Given the volume of negativity received we have decided to remove the pictures from the back of the buses within the next 24 hours."
A Welsh government spokesman said: "Whilst we are not responsible for the awarding of contracts for local bus services, we welcome the decision of New Adventure Travel to withdraw these adverts."