Morris Kleiner addresses how occupational licenses boost wages.
In the Middle Ages, guilds emerged to establish quality standards for crafts, and to protect the craftsmen from competition. A similar phenomenon -- regulatory capture -- is at work in some state capitals, with occupational guilds lobbying pliant legislatures to restrict access to their fields. According to a 2009 study by the economists Morris Kleiner and Alan Krueger, an occupational license provides a wage boost of about 14 percent, roughly similar to the increase attributable to union membership.
Bloomberg
September 16, 2012