The notes signed by "Miss R" beg the vets to find her pets new homes.
"My time is very, very short," the donor wrote. "There is not enough time to find homes for my children another way. I beg you not to let them die because I have to, please!"
"Please do not kill!" was written in capital letters on each of the containers.
Veterinarian Kim Bond said she found three plastic containers poked with holes sitting at her clinic's front door when she got to work at 7 a.m. a week ago.
Each cat's name, age, description and medical summary was written on its container. At least four other clinics received cats in Lee County, about 50 miles northeast of Montgomery.
"These cats were dearly loved," Bond told the Opelika-Auburn News. "They're not feral cats or neglected cats."
Most have new homes already. Veterinarian Buddy Bruce at Animal Health Center still has the six males dropped off Thursday at his clinic and he's offering discounts on all vet services, such as shots and neutering, to anyone who adopts one of the cats.
The identity and location of the donor is unknown.
"Other vets that I've talked to say the same thing, 'Let's do what we can to find these kitties homes,"' Bruce said. "These are her children. She took care of the situation the best way she could."