The group Free the Oregon Zoo Elephants encouraged Tomlin, who's long been known as an animal activist, to send the letter.
In the letter, Tomlin pointed to health concerns for the elephants, including the fact that one of their elephants Rama is infected with TB and Packy is also being treated for the illness.
"This is just one example of the problems elephants in captivity face," she wrote.
Tomlin mentioned a 2008 bond measure where the zoo called for an off-site multi-acre preserve for the elephants.
"It is now 2013 and the preserve is still not a reality," Tomlin wrote. "At 51, Packy does not have a lot of time to wait. So I implore you to give him a taste of real freedom and a chance to live out his days where he will be able to live like a real elephant."
On Friday afternoon, Oregon Zoo Director Kim Smith issued this statement in response:
"Here at the Oregon Zoo, we care deeply about elephant conservation and our future vision for our herd. More than 1.5 million people come to the zoo every year to be inspired by wonderful animals like Packy and his family. Packy is a geriatric elephant the oldest male Asian elephant in North America and he receives highly specialized care from our deeply dedicated keepers and veterinary staff. With more than half a century of experience caring for Packy and his family, our community zoo is renowned as a world leader in Asian elephant welfare. That legacy continues with construction of the expansive new Elephant Lands habitat here at the zoo, which will provide our elephants with unprecedented choice in the way they spend their daily lives."