An extra $14 paid to RSPCA staff on the days they euthanise animals is providing a "perverse financial incentive to kill" and may be driving up death rates, critics say.

The "euthanasia allowance" is detailed in the RSPCA's enterprise agreement which says it should be paid on each day that appropriately trained and certified employees are required to euthanise animals.

Kylie McCrea's son Jaiden with Rocket. Credit:Tracy Peters

Lawyers for Companion Animals principal Anne Greenaway said even hardened critics of the RSPCA had been shocked by the revelation.

"It's pretty weird, very weird, that for anyone who loves animals that an allowance of $14 is going to compensate for having to put an animal down, particularly when some of them are perfectly healthy," Ms Greenaway said.