Twenty of Hollywood’s biggest names, including Alec Baldwin, Susan Sarandon and Joaquin Phoenix, today sent a joint letter to McDonald’s CEO Steve Easterbrook, urging the company to institute commonsense animal welfare reforms advocated by the Humane Society of the United States.

The letter, which can be read here, is also signed by Vanessa Hudgens, Daryl Hannah, John C. Reilly, Mary-Louise Parker, Kristen Bell, Téa Leoni, Dr. Oz, Kate Mara, Stephen Fry, Mayim Bialik, Johnny Galecki, Joan Jett, Paul Feig, Weird Al Yankovic, Michael Showalter, Leona Lewis and Marco Antonio Regil.

“McDonald’s lets its chicken suppliers breed birds to grow so large, so fast it’d be like a two-month old human baby weighing over 600 pounds,” the letter states, adding: “This causes all kinds of problems for these animals—like broken legs, painful injuries, and even heart attacks.”

The letter is the latest salvo in the HSUS’s Unhappy Meals campaign, calling on McDonald’s to improve the treatment of chickens. We launched the campaign earlier this summer, starting with a television advertising campaign in Chicago, where McDonald’s is based. The results have been substantial. In addition to capturing the attention of Hollywood, more than 10,000 individual consumers have placed calls to McDonald’s urging the company to do better.

Unfortunately, McDonald’s has yet to make meaningful progress. As a result, we’re going to extend our ad campaign, engage more online advertising channels, and we are pursuing other actions calling on McDonald’s to do better.

This is more than a campaign for us; it’s a mission. And we will continue fighting for these chickens until McDonald’s—and all other food companies—pledge to improve their practices and the welfare situation of the billions of animals concerned.

Take action at UnhappyMeals.com