Cat Haven and RSPCA are reminding people to sterilise their cats before cat breeding season hits in August.
RSPCA Spokesperson Tim Mayne said members of the public could make a big difference and minimise the high number of cats coming into shelters at Christmas by sterilising their pets now.
"Unclaimed cats, which people often feed but don't consider their own cat, are also a big problem," Mr Mayne said.
The animal welfare groups are also calling on people who feed them to take responsibility for getting them sterilised.
Cat Haven Spokesperson Jessica Reid said thousands of unwanted kittens were received by cat shelters last Christmas and with not enough homes and nowhere for the surplus to go many of them had to be euthanised.
"If more cats were sterilised before the start of breeding season this awful situation could be prevented," Ms Reid said.
Australian Veterinary Association WA President Garry Edgar endorsed the call.
"Some people need to be more responsible for the cats they are feeding." Dr Edgar said.
"Semi-owned cats that are being fed by irresponsible people are often the source of these unwanted kittens.
"Do not just feed a cat, desex it and let it become a pet for life."