Nurseries which don't offer a plant-based alternative to cow's milk are indirectly discriminating against children, according to The Vegan Society.
The Nursery Milk Scheme, which was established in the 1940s, offers free cow's milk to children under 5 in nurseries - but parents of plant-based kids have to pay for their alternatives.
Now The Vegan Society has written a formal letter to the Department of Health saying 'nutritional public health initiatives for children must include fortified plant milk to cater for the growing number of vegan children'.
"Law regulating the provision of milk for young children is in urgent need of reform to recognize current scientific evidence on nutrition and a growing consumer trend away from dairy products," Jeanette Rowley, The Vegan Society's legal advisor, said.
"Public authorities are under a general duty under the Equality Act 2010 to avoid discrimination; by limiting the Nursery Milk Scheme only to cow's milk, the Department of Health are failing in that duty.
"We are urging the government to include fortified plant milk in its milk schemes nationwide, to ensure vegan children are catered for with a nutritionally adequate and delicious milk alternative."
"Vegan children are unfairly treated as they do not benefit from the current school health initiatives, which are designed to increase calcium intake for growing children," added Mark Banahan, Campaigns Manager at The Vegan Society.
"They often miss out or have to rely on parents to provide their own plant milk, something that is not always possible for low-income families and causes a great deal of inconvenience to families who should be entitled to free milk alternatives.
"It's time the government Play Fair with Plant Milk and support it in nutritional public health initiatives for children."
The charity has given the Department of Health 14 days to respond, after which it will be considering legal options.
*The headline of this article was updated on November 26. An earlier headline incorrectly stated that campaigners would sue nurseries, rather than the government.