New York City Animal Care & Control is suspending euthanasia for a day as part of a nationwide event called "Just One Day."
AC&C says it will not perform euthanasia on Wednesday unless it is medically necessary.
It has extended adoption hours and reduced fees.
Area rescue groups are also making extra efforts to help move pets out of the city's shelters.
AC&C takes in about 30,000 animals a year. It says that last summer it took in nearly 6,000 cats — enough to fill about every seat in Radio City Music Hall.
The organization says that in April, it had a live release rate of 86 percent, its highest ever. That includes adoptions, reunions with owners, and transfers to other nonprofits that help find homes for the animals.
AC&C operates shelters under a contract with the city.