There's a convention in town, and one of the conventioneers goes looking for a whorehouse. He finds one and asks the madam, "Is this place union?" She says, "No, my girls don't need any union, sir." He says, "Well, I only patronize union whorehouses," and he storms off. He repeats this scene at several other places, and finally he gets to the last bang shack in town.
He asks the madam, "Is this place union?"
She says, "You bet it is. This is the only unionized cathouse in town."
He takes out a wad of twenties and says, "All right, I'd like your youngest, perkiest, most luscious girl."
She says, "I'm sure you would, sir, but Cora's been with me for 37 years, and she has seniority."