Ann Kirton, who runs St Francis Animal Rescue, in South Shields, says she has noticed an increase in the number of litters handed over to her - especially in recent months.
She fears some unreputable owners are purposefully allowing their cats to become pregnant in order to sell the kittens online.
However, a large number are being born outside and becoming feral.
She has now re-launched a neutering scheme in the hope of putting a halt to the rising numbers of young kittens being born and left homeless.
Ann, who has run a rescue shelter for abandoned cats for more than 30 years, said: “It is really worrying. The number of kittens being found abandoned on the streets is going up and it’s concerning.
“I’ve seen a lot of kittens being sold on websites and most of them haven’t been defleaed, wormed or neutered and they should be.
“The issue isn’t getting any better at all.”
In a bid to help combat the problem, Ann is offering free neutering for cats for owners who are on benefits and low incomes.
Ann added: “I have done this scheme before and I’m doing it again, in the hope it might make a difference.
“It’s not just for people who are on benefits but also those on low incomes.”
The scheme is supported through money raised by the charity created by Ann. It relies heavily on donations and is run with the help of volunteers - some who foster cats and kittens until they can be found their own forever home.
The charity has a shop in Stanhope Road selling a range of items to help raise funds for the animals it cares for.
For more information on the free neutering scheme, or advice on spaying and neutering call Ann on 456 9613 or 07528 245 088.
• A number of cats and kittens cared for by the charity are ready for adoption.
For details visit www.stfrancisanimalrescue.co.uk