ASPCA does not support s/n laws -

ASPCA Position Statement on Mandatory Spay/Neuter Laws - 
The ASPCA does not support laws that mandate spay/neuter of all owned animals within a community; however, based on currently available scientific information, the ASPCA strongly supports spay/neuter as an effective means to reduce shelter intake...

In summary, the ASPCA recognizes that sterilization is currently the best method to reduce companion animal overpopulation and therefore to reduce shelter intake and euthanasia. The most important step a humane community can take to decrease companion animal overpopulation is to make a safe, effective, voluntary spay/neuter program available and readily accessible to the community, and create programs and incentives targeted to the populations known to be contributing disproportionately to shelter intake and euthanasia.

www.aspca.org/position-statement-mandatory-spayneuter-laws