In a world with scarce resources, everybody competes. It is just who you compete with... Author attempts to say that the union is one group against management, while non-union compete against each other.

Another view is that white collar employees do there best for their employer--thus competing against the employers' competitors. The incentive for doing so is that a rising tide often raises all boats... (See e.g. http://www.wsj.com/articles/behind-rising-inequality-more-un...) This would lead you tho the conclusion that only an idiot competes within their own company.

Alas, as always, the truth is somewhere between the two extreme viewpoints.