Whenever a city or county requires cat license tags, any such tag shall be issued for one-half or less of the fee required for a cat, if a certificate is presented from a licensed veterinarian that the cat has been spayed or neutered.
Source:
Section 31751.5, https://leginfo.legislature.ca.gov/faces/codes_displaySection.xhtml?lawCode=FAC§ionNum=31751.5..