The Vegan Society has told the NHS it must overhaul its Healthy Start scheme to include vegan-friendly milks and vitamins.
The scheme offers vouchers to families and pregnant women on benefits that can be exchanged for milk, vitamins and fruit and vegetables.
But parents are restricted to buying plain cow's milk that is whole, semi-skimmed or skimmed.
Milk substitutes such as almond or soya milk cannot be purchased.
Now, the Vegan Society has written to NHS officials saying the scheme is discriminatory and adding that vegan-friendly vitamins should be made part of the scheme.
The letter said: "The convictions of vegans come within the protection of the law and, on the face of it, it appears that the Healthy Start voucher scheme could be inadvertently discriminatory."
It added: "It is important for everyone to eat calcium-rich foods daily and fortified plant-based milk plays an important role in vegan nutrition.
"In fact, the UK's Eatwell Guide recognises that fortified plant-based milk represents a valuable alternative to cows' milk.
"Calcium content is comparable and the soya variety is similar to cow's milk in terms of protein quantity and quality.
"Another issue that affects vegans is that Healthy Start supplements contain vitamin D from animal fat, which means that the only vegan-friendly nutritional benefit of this scheme is free fruit and vegetables.
"In order to meet national recommendations about supplementation of vitamins A, C and D in under-fives, vegan parents/guardians have to purchase vegan-friendly drops."
The letter said the vitamin D supplement currently on offer "unfairly disadvantages vegans and the restriction on the purchase of milk is unjustified."
It also warned that the NHS "must give due regard to the needs of vegans to ensure compliance with legal duties, and so that vegans do not experience unlawful interference or discrimination."