Lilly’s should be labeled that they are TOXIC to cats.

Unfortunately, several types of lilies have been found to be deadly to cats, including Easter lily, tiger lily, rubrum lily, Japanese show lily, some species of day lily, and certain other members of the Liliaceae family. Ingesting just one leaf can result in severe poisoning, and within a very short time your cat will exhibit signs of toxicity.

All parts of the lily plant are considered toxic to cats, and consuming even small amounts can cause severe poisoning. Kittens are particularly prone to being poisoned as they explore their environment, and older cats are often affected simply because they brush against the flower and get pollen on their coats. Later they groom the pollen off, and of course ingest the lily pollen as they clean their fur.
Symptoms and Treatment 
The primary toxic effects are on the kidneys. Within minutes to hours of ingesting part of the lily plant, your cat may vomit, become lethargic, or develop a lack of appetite. As the toxin begins to affect the kidneys, these signs continue and worsen as the kidney damage progresses. Without prompt and proper treatment by a veterinarian, the cat may develop kidney failure in approximately 36-72 hours.
If you see a cat eating lilies, contact a veterinarian immediately. If emergency treatment is begun within 6 hours of consumption, the chances are good that the cat will recover. This generally consists of emptying the gastrointestinal tract of the affected cat and intravenous fluid therapy in a hospital setting. If more than 18 hours has elapsed, and the kidneys have been severely affected, your cat may not survive, even with emergency care.
The treatment generally consists of hospitalization and intravenous fluids. Your vet may also give your cat medication to control nausea and vomiting. Home care will not result in full recovery.
Prevention   Unfortunately the only way to prevent your cat from eating lilies, and to ensure they're don't suffer any of these effects is simply not to have lily plants in your home.