It was only a regulation for air travel -- the general assumption seems to be that cats refuse to wear collars, and you can't make a cat do something it doesn't want to do. :-) For example, here in the US, you're legally obligated for any damage done to someone else's property by your dog, or horse, or cow, or goat... but not a cat. Because it's recognized that we humans have little or no control over them. If they do things we ask them to, it's because they love us and want to make us happy. Not because they take orders.