unions as a "minority group"

Check out this odd sentence in an otherwise enjoyable review of the movie Milk-- by Sara Havens in LEO...

Milk fought for the rights of other minority groups, including union workers.

In one sense, union workers are members of a minority group. See also: Cincinnati Bengal fans, those who like anchovies on pizza, those who drive Fords, etc.

But typically, the term is employed to imply persecution or suffering. And that certainly cannot be said of those in labor unions. In fact, one could easily say the opposite is true in most cases. As members of a cartel, we would tend to say that those in a cartel have heightened bargaining power with those who purchase their goods and services. Are the nations of OPEC a minority group?