Name a multi-billion dollar industry where all the competitors in the industry have formed a single cartel. This cartel performs many functions, but one of its highest profile functions is to aggressively punish any member who pays its employees more than a cartel-enforced maximum.
Believe it or not, there is such an industry in the US... college sports. The cartel is the NCAA, and whenever the NCAA makes the news, it usually is with an enforcement action punishing a school for allowing any of its athletes to make more than the agreed maximum salary, which is generally defined as free tuition. As folks are learning at Ohio State, even trading your autograph for a free tattoo is not too small a transaction to attract ruthless NCAA retaliation.
This ESPN page (via Phil Miller) shows 2010 athletic revenue by school. Take the top school on the list, the University of Texas. In 2010 its athletic program brought in over $143 million in revenues. It paid its workers (athletes) who helped generate this revenue $8.4 million (in the form of tuition), or 5.9% of revenues. Its hard to decide whether this is high or low, though this percentage of labor for a service business seems low. Looking for an analog, we can turn to the NFL, which is currently negotiating a revenue split with players. The issue is still under negotiation, but for years players have been guaranteed over 50% of total revenues.
Even the Olympics finally gave up its stupid distinction of amateur status, allowing the best athletes to compete whether or not someone has ever paid them for anything. This only makes sense - we don't have amateur engineers who work for free before they give up their amateur status for the professional ranks. I can still continue to earn my degree at college in programming while being paid by outside companies to do programming. I can still participate in the school glee club if I make money in a bar singing at nights. I can still be student council president if I make money in the summers at a policy think tank. Of all the activities on campus, the only one I cannot pursue if someone is willing to pay me for the same skill is athletics.
Only the NCAA holds out with this dumb amateur distinction, and the purpose is obvious -- it provides cover for what otherwise would be rightly treated as worker exploitation. And they get away with it because most of the members of this cartel are actually state governments, who are really good at exempting themselves from the same standards the rest of us have to follow.