In a highly competitive marketplace, it becomes difficult for unions to sell their labor with promises of higher quality… especially since unionized labor is notoriously difficult to work with, due to the productivity-limiting rules mentioned above, and the way union representatives insert themselves as a layer of bureaucracy between workers and management. Organized labor is a lot more expensive than hiring individual workers. They don’t cost five or ten percent more – they often cost two or three times as much to employ. It’s hard to convince employers to pay this much voluntarily.
This leaves the union with only one other method of preserving its collective bargaining power: it must limit the ability of non-union workers to compete with its members. That is why organized labor is so desperate to get the “Card Check” legislation Democrats promised them. It would remove secrecy from union votes, enabling the union to pressure independent workers into joining up. There is already a law known as the Davis-Bacon Act, passed in 1931, that prevents non-unionized operations from under-bidding union shops for government contracts. Union shops would almost never win competitive bids for public works projects otherwise.
Organized labor is heavily depending on political interference in the free market for success, because only political power can effectively shut down competition. Collective bargaining only works if the union has a functional monopoly on providing labor to the employers it negotiates with. Threats of a strike are only effective if employers cannot simply fire the striking workers and replace them.
Monopolies are extremely difficult to create without government intervention. Government power is even deployed to force people to join unions. For example, last year in Flint, Michigan, independent day care providers suddenly discovered that union dues were being subtracted from the state child-care subsidies they depend upon, and remitted to an organization created by AFSCME and the United Auto Workers.