Obi-wan - I'm not a poker player myself, but I believe the game refers to moves similar to the letter going to the IRS as a bluff.  Personally, I would never write a letter like that, but it probably is good enough to get some folks nervous enough to get their bill paid up.  The only good thing about going that route, you probably aren't going to serve as much time in jail as you would breaking someone's kneecaps - the more common bill collecting technique.