Peterborough Cat Rescue is able to deal only with emergencies
Unneutered cats are costing pet owners money, according to a charity that is being "inundated" with calls.
Peterborough Cat Rescue said it could deal only with emergencies as the city's feline population continues to grow.
The cost-of-living crisis and increases in vets' bills are thought to have contributed to the problem.
Jo Underwood, who has cared for more than 600 cats over nine years, has encouraged more people to foster.
The 49-year-old, who is a foster co-ordinator with the charity, said the group had to prioritise pregnant female cats and kittens because of the pressure on volunteers.
"In Peterborough, the cat population seems to be expanding. It is getting worse and worse each year," she said.
"Unneutered male cats are fighting, spreading disease and costing cat owners more money.
"It is also mating season, so we get daily calls about cats being found with kittens."
Once rescued, kittens have to be fostered for nine weeks before they are vet-checked and then rehomed.
Volunteer fosterers can choose how many cats to care for. Ms Underwood once looked after 14 at the same time.
'Frustrating and timewasting'
She said fostering gave her teenagers a sense of responsibility, and it was rewarding work.
However, "frustration has been high" among some carers after they were "messed around" by potential adopters, she added.
In a warning it issued on Facebook, the charity said: "Only apply if you are 100% committed and [have] not just fallen in love with a cute kitten on Facebook.
"We've had 10 applicants change their mind post-viewing or wanting to adopt, far into the process.
"Another 17 applicants have not responded to our messages and calls after wanting a cat."
The charity added that those 27 applications had been vetted by three volunteers who were juggling their time around their families and their own full-time work, and being let down that way was "incredibly frustrating and timewasting".
Ms Underwood said a number of people were giving up their cats after they get pregnant, and she added that the cost-of-living crisis and increases in vets' bills might have contributed to the number of rescues the charity was carrying out.
Follow East of England news on Facebook, Instagram and X. Got a story? Email eastofenglandnews@bbc.co.uk or WhatsApp 0800 169 1830
