You can't separate public and private unions

Ezra Klein:

Unions are not just about challenging the "might and greed" of private-sector CEOs, but about recognizing the different incentives faced by managers and workers, and about correcting the tremendous power imbalance between those who can be fired for asking too many questions or demanding a different bargain and those who get to do the firing and would prefer a more submissive workforce and a status quo that they've created and defined.