Some Hamilton pet owners will need to get their pets re-microchipped after a possible fault was found with Virbac BioTec microchips fitted between 2009 and 2012.
Microchipping is a key way a pet can be identified and safely returned home if it gets lost.
Virbac are urging any dog owners who may have one of the potentially affected microchips to visit their local vet and get a new microchip. It's only the one type of microchip affected, there are many kinds, and Virbac are covering the costs of the new microchip.
Cat owners should also be checking their pet's microchip.
Hamilton City Council Animal Education and Control Manager Susan Stanford says they're doing what they can to let potentially-affected dog owners know.
"We're proud Hamilton has the highest rate of microchipping in the country and want to make sure they're all working well," said Ms Stanford.
"We have identified it affects about 850 of the 11,500 dogs currently registered in Hamilton and we will be sending out notifications to these owners."
"Some of the chips could be working now but may stop working later. The risk of the chips being faulty is very low but it's always better to be safe than sorry as you never know when it could be the only thing helping us know who the owner is."
"We've been able to rehome two dogs who have been away from their homes for a long time only because they were microchipped. We cannot stress how important it is to have your dog microchipped.
Cats who are trapped and sent to the vets will be at most risk of not being returned home. It is then up to the different vets to decide the fate of the cat.
Cats who have been killed away from home and picked up by the Hamilton City Council will be held for two days for an owner to come and collect them. If they are not collected the council will dispose of them.
"If the microchip number of your pet starts with these numbers: 90008800xxxxxxx, 900008800xxxxxx and 900001000xxxxxx contact your local vet to have a second microchip inserted and registered. Don't forget to also send a copy of your new microchip certificate to Animal Education and Control."