The AMA is totally a guild and its primary mission is to limit the number of people able to practice of medicine, thereby driving up doctors' salaries. They do

The AMA is totally a guild and its primary mission is to limit the number of people able to practice of medicine, thereby driving up doctors' salaries. They don't need to organize as a formal union because the federal government actively sets the number of doctors in the U.S., so they can manipulate public policy instead. I can tell you first-hand that AMA lobbied hard to reduce the number of medical school slots in America, there actually was an AMA-backed federal program in the mid-1990s that paid schools for the lost revenue from being forced to admit fewer students! The AMA also works to prevent nurses and midwives and the like from performing simple medicine and competing with doctors.