A group called Overweight Haters Ltd has been giving the cards to unsuspecting men and women on the underground at Warren Street and Oxford Circus stations.
On Saturday, Kara Florish, from Southend-on-Sea in Essex, was travelling on the tube to Euston to meet her family and was handed one of the fat-shaming cards.
She took a photo of the hateful leaflet and posted it to Twitter, saying; 'Was handed this card on the underground. Is hateful + cowardly + could potentially upset people struggling with confidence.'
The card reads; 'Our organisation hates and resents fat people. We object to the enormous amounts of food resources you consume while half the world starves.'
'And we do not understand why you fail to grasp that by eating less you will be better off, slimmer, happy and find a partner who is not a perverted chubby-lover or even find a partner at all.'
Kara, who works for the NHS and is also a trained classical singer, was not the only one to be handed the notice in the capital.
Sean Thomas Knox witnessed the 'stunned, desolate reaction' when a fellow passenger was left crying after being handed the leaflet.
Young man just got on train at Oxford Circus, gave printed card saying YOU'RE FAT to overweight girl. He jumped off. She read it, & cried.— sean thomas knox (@thomasknox) November 30, 2015
Writer Sean, who is followed by TV presenter Stephen Fry on Twitter, described the perpetrator as 'a hipster, smartly, trendily dressed' with a beard.
Sarcastically concluding; 'Perhaps it was a piece of conceptual art. Wanker'
The card goes on to say that the group opposes the treatment of people with obesity-related health problems on the NHS, as it is a 'waste' of money.
Kara told the Daily Mail; 'I am not upset myself... I am smaller than the national average and not exactly obese, but this is hateful and cowardly and could potentially upset people struggling with confidence and eating disorders.'
Many big names have supported Kara's decision to speak out, including beauty brand Dove UK who replied to her social media post saying; 'We salute your bravery #speakbeautiful'
The British Transport Police are now investigating the reports and urging anyone with further information to come forward.