The travel firm has upset some customers with its in-flight entertainment packs.
While the activity sheets and stickers were handed out as a kind gesture, many have accused the airline of treating male and female children differently.
One customer hit-out at the airline for giving boys “Future Pilot” stickers, while all the girls she saw had ones that said “Future Cabin Crew”.
Dame Gillian Morgan, 65, noticed the stickers following her flight to Bristol from Paphos, Cyprus.
In an interview with Metro, she claimed she was “absolutely sure” that the badges were being handed out based on gender.
The holidaymaker accused TUI of being “deeply sexist” , commenting: “It happens implicitly all the time. The boys can have the Lego, the space rocket going to the moon, and the girls can have a little pony.
“We desperately need more women to do science, maths and engineering but little things like this take us backwards by providing restricting roles.
“It actually stops us as a country, getting the best out of our workforce.
“In 30 years time it might be likely that the majority of pilots will still be men but we should not be turning off the girls who are going to be the ones to walk on Mars.”
OH BOY: TUI were accused of handing 'cabin crew' stickers to girls and 'captain' ones to boys
Dame Morgan wasnt the only customer to complain about the policy.
One passenger tweeted: “@TUIUK your cabin crew today chose future TUI cabin crew stickers for the girls and future pilot for the boys, no female pilots then?”
Another traveller: “Lovely touch by @TUIUK flying out to Corfu Friday by giving children TUI stickers and activity sheet.
“Not so lovely that all the boys were given future pilot stickers and the girls 'future cabin crew'?! Sexist much?"
Following the complaints, a TUI spokesperson said that stickers were not handed out on a gender basis.
They said: “Were sorry to hear a small number of customers have been upset by this.
“We think it has just been a simple mix-up since our future pilot and cabin crew stickers are designed for use for any child regardless of gender.
“The stickers are part of our activity packs which are intended to be used by crew to interact, engage with and create special moments for our customers on their holiday.
“The feedback weve had so far this summer has been overwhelmingly positive.
“Children fall in love with flying when they go on their holidays with us and we want to encourage their dreams of becoming future pilots and crew members.”
It's not the first time British consumers have complained about sexism.
Two lingerie brands recently came under fire for their campaigns.
Beldona was criticised for a billboard that displayed the enterity of a female model's behind.
And Silks, a Glasgow-based store, upset shoppers with their "overly sexual" promotion.