The cereal giant currently uses a version which is derived from lanolin - which comes from sheep's wool.
Now more than 2,000 people have signed a petition urging Kellog's to switch to vitamin D2 or a plant-based vitamin D3.
The petition was initially launched by Herbivore Club - which has partnered animal rights Animal Aid - to run the campaign jointly.
It says: "Vegans avoid wool and products made from wool for a number of reasons. Firstly, there is an inherent link between the wool industry and the meat industry.
"Additionally, undercover investigations into the wool industry have shown abuse and horrific treatment of gentle sheep during the shearing process."
'Never been a better time'
"At a time where many people are either adopting a plant-based diet, or wanting to incorporate more vegan food into their diets, it has never never been a better time for companies and businesses to increase their vegan offerings," Animal Aid Campaign Manager, Tod Bradbury, said in a statement sent to Plant Based News.
"Whilst Kellogg's does have some delicious vegan cereals, by making this very small change which will not compromise on taste or quality, they will be opening themselves up to the biggest growing market.
"This very simple move will make many Kellogg's products suitable for vegans – and indeed anyone else. There is no downside."
'Future-proof its business'
"Plant-based eating is on the rise with consumers becoming increasingly aware of the impacts of animal agriculture, and questioning the ethics of farming animals," added Adam Shaw, of Herbivore Club.
"Many companies are taking note of this shift in recent years, and are adapting to meet demand. Kellogg's has an opportunity to future proof its business by providing more inclusive products."