Is it against the law to threaten the life of a dog for money?

I'm not going to do this, but i just had this random thought the other day. What if some guy who could give a care less about dogs put an ad in the local paper with a pic of his dog saying "I'm tired of this mutt, if someone doesn't pay me $500 dollars by next week I will take out to my property and put it down" Is that legal? I mean it's not kidnapping a person or something, I know killing a dog might be a crime in someplaces, but geez say it's a guys ranch in the middle of nowhere. I figure some do good er' peta type would rush in and put up the money.