They make $200 a day at the USO. No wonder players run roughshod all over them. For the sake of comparison, NBA and NHL referees make between $100K and $300K annually. NBA refs have enough money and power to make the lives of recalcitrant players a nightmare: calling fouls at the slightest contact, giving opposing players makeup calls, ejecting players with a history of abusive behavior ejections at the slightest provocation. Yes, the NBA refs have a union. What if tennis umpires were to form a union? Any obstacles to this?