I'm all for this law.
Everyone knows that there are thousands of dogs and cats out there who would like to have a forever-home. Not just mutts and alley cats, but purebreds too. There are even shelters that only specialize in certain breeds. Sadly, many shelters are full to overflowing with animals. Some even have to turn away animals, as they are too full.
On the other hand, some animals in pet shops are from puppy/kitty mills - places where animals are bred only to sell and make money (and not just certain breeds). These "mills" don't care about animals (their health, welfare); they just want to make money. (Note: not all animals are from mills and not all pets shops buy from mills). This is what the new law is trying to prevent.
Unfortunately, many times the price paid at a pet shop is higher than the price paid at a shelter - for the same animal. This may discourage folks from buying pets at a pet shop. Having worked retail for many years, I know that retailers are always looking for ways to "skirt laws" (loopholes) in order to boost their profits. Some pet shops may stop selling dogs and cats altogether.
If you want dog or cat, skip the pet stores and visit your local shelter. Some shelters will even call around to other shelters to help you find the “purrfect” companion.