The Society for the Prevention of Cruelty to Animals has been accused of being overly zealous in trying to control the feral cat population - its vets apparently tried to neuter the same stray twice.
The case emerged on the internet after a video clip of a cat with both ears clipped was widely circulated on Facebook.
Its vets generally clip off a small part of a stray cat's ear while it is being neutered and under anaesthetic to indicate that the procedure has been done - left for females and right for males.
The domestic short-haired cat in question is a six-year-old male called "Ice-cream Boy".
The video features Mary Wong, a volunteer who cares for stray cats and noticed the moggy at an SPCA centre on Saturday. She uploaded the video onto her personal Facebook page.
"Both of your ears are clipped. So are you a boy or a girl now?" Wong asks the cat in the video.
Internet users say his clipped ears are evidence of a medical blunder on the part of the SPCA.
One animal lover wrote on the Facebook thread: "[My] heart breaks!" Another said it was a case of "fresh graduates" coming to the SPCA in Hong Kong to get experience as vets, only to "treat stray cats like white mice".
According to Wong, the cat was castrated several years ago through the SPCA's Cat Colony Care Programme. She said he was caught again two weeks ago and transferred to the SPCA by the Agricultural, Fisheries and Conservation Department.
The programme was set up by the SPCA in 2000 to try to stabilise and eventually reduce the number of stray and feral cats in the community via a co-ordinated trap, neuter and release effort.
An SPCA spokeswoman said yesterday that she could not comment on the case as the programme's vets were on leave.