Vets sometimes get asked to put down healthy animals because owners no longer able or want to keep them, the Veterinary Council says.
A Facebook post showing a healthy cat that was taken to a vet for euthanasia has drawn attention to the practice, which one vet said worsened as the holidays approached.
The council said sometimes euthanasia would be asked for when an elderly owner was entering a resthome or someone had developed an allergy to a pet.
Council spokesperson Wayne Ricketts said most vets would avoid putting down a healthy animal.
"We just don't like it and we certainly don't like euthanising animals because their owners become sick of them or they no longer want them."
He said many vets would instead try to rehome a pet, often at their own cost.
Vet Heather Remnant said her Christchurch practice, At the Vets, saw more healthy pets facing euthanasia in the lead up to the Christmas holidays.
"People will come in and they'll tell us that an animal's elderly, not doing that well and they want it put down. On exam we'll discover that the cat's five years old and, in fact, in quite good health."
Most owners in this situation were at their wits' end as a result of a change in circumstances, such as a marriage break-up or a move overseas, Ms Remnant said.
"We got an awful lot of them after the earthquakes when people were trying to find rentals and they couldn't get rentals with pets."
Many of those owners wanted their pets euthanised because they couldn't not see another outcome for their animals, she said.
However, her vet practice worked with animal welfare groups and managed to rehome all the pets in other parts of the country.
There were some cases that haunted her, including that of an aggressive, divorcing couple who were determined that neither should get to keep their cat.
"So the only option that they could see was that the cat went to heaven and that was a way of hurting each other.
"Occasionally you get stuck between a rock and a hard place and you have to do these things, but you don't forget them."
The Veterinary Association said vets could refuse to euthanise a healthy pet but only if they were sure the animal's wellbeing would not be compromised as a result.
Spokesperson Helen Beattie said often the reasons for putting a healthy pet down were legitimate but it was not something that a vet would take lightly.
"I think most veterinarians would feel pretty uncomfortable about there being any sort of friviolity with respect to an animal's life just because because it didn't suit."