The american medical association, a physicians' union, is a good example of a(n):

The American Medical Association, a physicians' union, is a good example of a craft union.

Explanation:

A craft union is a group of workers of the same profession who come together to defend their interests.  It differs from the branch union in that it represents workers of the same proffesion, such as teachers, electricians, plumbers, etc., instead of workers of different trades within the same branch of production.

answer; conflict perspective;