A nice point made in this column, titled The Road to Fiefdom:

"Because their jobs are on the line in every election, government workers are especially mobilized in politics."

I've often heard and repeated the point that government employee unions represent a monopoly of a monopoly: since there's nowhere else to get law enforcement, or a new driver's license, or a third-grade education (for most, anyway), the government has an effective monopoly over those services. The unions representing those employees effectively have a monopoly on the labor which provides the service over which the government has a monopoly.