The Umbrella hitmaker courted controversy by posing for pictures with what appeared to be two giant marijuana joints during a night out in the city last weekend.
The snaps were posted on Rihanna's Twitter and Instagram pages, and now campaigners want River Island executives to end the singer's contract with the fashion company.
Lucy Dawe of the Cannabis Skunk Sense group tells the Daily Mirror: "She should be dropped by River Island as she's a role model to young children but clearly an appalling one.
"It is a huge double standard because if River Island were really concerned about the effects of drug use, they wouldn't be supporting someone who is so blatantly using drugs herself."
Another image posted by Rihanna appeared to show the star smoking weed in her hotel room with the words, "Legalise it", and Paul Jenkins from the charity Rethink Mental Illness has taken aim at the singer for her attitude.
He adds: "She is reinforcing the myth that cannabis is a 'safe' drug, when in fact it can increase your chances of developing mental illness, especially if you use it when you're young. It's disappointing to see Rihanna normalising cannabis use in this way."
Rihanna designed a clothing collection for River Island earlier this year, and she is reportedly working on a follow-up line.