Paul McCartney wants to see the prices of plant-based kinds of milk fall in line with Starbucks’ more traditional offerings.

Starbucks, the biggest revenue earner among fast food chains, currently charges 70 cents for consumers to use oat, almond, soy and coconut milk The Beatles legend, in conjunction with People for the Ethical Treatment of Animals (PETA) penned a letter to Starbucks CEO Kevin Johnson. McCartney’s letter to Johnson was shared with Billboard.

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It recently came to my attention that Starbucks in the USA has an extra charge for plant based milks as opposed to cow’s milk,” McCartney wrote in the letter. “I must say this surprised me as I understand that in other countries like UK and India, there is the same charge for both types of milk and I would like to politely request that you consider this policy also in Starbucks USA.”

“My friends at PETA are campaigning for this to happen and I have agreed to support them with the quote: ‘Sir Paul is asking Starbucks to end its surcharge on plant milks,’ and I sincerely hope that for the future of the planet and animal welfare you are able to implement this policy.”