In much of the United States, there is a concept known as a "Right to Work" law. It simply says that unions may not require union membership as a precondition of working at a facility. It doesn't disallow the union, but it doesn't force it either.
Unions argue that this "free rider" problem is a huge blow to Union power. This was so much the case that when Michigan just recently passed such a law, near riots broke out.
In any event, union membership has declined from its highs in the 1950s to a mere 11% nowadays - its lowest point since the 1930s. Regardless of whether you like them or not, there is at least a plausible case to be made that these laws serve as a (either healthy or horrible, depending on your perspective) check on union power.
In "Union 1.0," once a workplace voted to organize, it effectively becomes a monopoly, requiring anyone who wishes to work at that facility subsidize the union. My wife, for example, as a teacher, can in many states, be required to financially support the NEA, even if they are promoting things that are exactly contrary to what she and I believe. Right to work does not compel such union subsidies, meaning that my wife would not, say, have to quit her job on principle. She could simply choose not to support the union. As such, the union has to not overreach, serving that useful check.