H.S. honchos are pissed off after reading that Spears went to a pet store in fancy Bel Air, Calif., and dropped three grand on a Yorkshire Terrier. The Humane Society has been dogging pet stores, claiming many of the pups come from puppy mills.

H.S. is also really upset that Spears spent only 30 minutes before sealing the deal -- "Choosing a dog is a major lifestyle decision that should not be taken lightly." Apparently, the Humane Society thinks Brit might pull a Paris -- as in getting bored (after all, she does have ADD) and jettisoning one pooch for another.