(NEXSTAR) — Paul McCartney doesn’t care too much for money — unless he’s being upcharged for non-dairy milk.

McCartney, a longtime vegetarian and animal-rights activist, recently penned an open letter to Starbucks CEO Kevin Johnson, urging him to end the chain’s surcharges for alternative milks.

The legendary musician issued his statements in partnership with PETA, which has previously called out the practice for penalizing customers “who are making the humane, environmentally friendly choice.”

“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 U.K. 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 … I sincerely hope that for the future of the planet and animal welfare you are able to implement this policy,” he concluded the letter.

In a press release issued this week, PETA added that McCartney is hoping to change Johnson’s mind before the latter’s retirement on April 4. Former Starbucks CEO Howard Schultz will be stepping in as interim CEO, the company announced.

PETA has long campaigned against Starbucks’ surcharge for plant-based milk, arguing that it not only contributes to the support of dairy farming, but unfairly discriminates against vegan customers. Also affected are lactose-intolerant customers, “most of whom are people of color,” PETA has previously said.

Starbucks itself has also acknowledged that “dairy is the biggest contributor to Starbucks carbon footprint” — another point that PETA is quick to repeat.

In this week’s press release, PETA added that a number of national chains, including Panera Bread and Pret A Manger, have already eliminated surcharges for non-dairy milk.

A representative for Starbucks was not immediately available to respond to McCartney’s letter. But Starbucks said as recently as Nov. 2021 that it was working on new approaches to sourcing sustainable dairy, but did not announce any plans to scale back on dairy offerings or make it more affordable for customers who request non-dairy options. The chain did, however, say it would continue to introduce more plant-based menu options.

The production of dairy, meanwhile, continues to have “a higher environment impact that all of the alternative milks,” according to an article published by the University of California, Davis, which cited (among others) a study from researchers at the University of Oxford.