Sisters Rooney Mara and Kate Mara are using their Hollywood star power for good!

The talented actresses have written an open letter to the New York Blood Center in response to their "abandonment" of more than 60 chimpanzees in Liberia. After the organization withdrew their support of the animals after more than 30 years, the Mara sisters believe they have left the creatures to survive on their own without food or water.

"As you are aware, when you withdrew all support for these chimpanzees one year ago, you left them in a life-threatening situation," Rooney and Kate wrote in their open letter to the President and CEO of the New York Blood Center. "If it had not been for the dedicated caretakers and emergency care from nonprofit organizations like The Humane Society of the United States and Humane Society International, these chimpanzees would surely have died horrible, slow and painful deaths from dehydration and starvation."

Recently, the Mara sisters were able to travel to Liberia where they visited the chimpanzees and their dedicated caretakers. With the help of The Humane Society, the animals have been able to defy expectations. Unfortunately, it's costing the organizations upwards of $20,000 per month.