American Medical Association and various state medical boards, various legal bars, AICPA, CFA Institute, various academic accreditation institutes form a kind of network that even accredits colleges that still practice alumni preference (almost all of them)--a sort of union seniority rule that extends beyond into familial offspring.

Most upper-middle class stuff is heavily protected by union like organizations, many of which restrict membership count and lobby against immigration in their field based on maintaining salary levels and their standards of living.