It isn't. Unions themselves are a borderline criminal practice, that we tolerate because collective bargaining is sometimes the only way to redress serious issues in the short term. There is no "company town" scenario for government employees, and they cannot suffer under the same working conditions of the meat packers and coal miners and other such people whose trevails made unionization acceptable.

Basically, a union is the exact same practice that would be called "collusion" if the people who did it owned or rented buildings. A worker is a merchant who sells (his) labor. When he goes on strike, he is stating that he requires a certain degree of remuneration for his labor, and will not sell it for less. When he gets together in a union to strike, he & his fellow merchants are agreeing not to sell their labor below a certain price. The purpose of a picket line is to threaten and harass those who are willing to sell at lower prices.

Now try to imagine everything I said, applying to local grocery and convenience stores selling milk. What if all the store owners in a community got together and agreed on a price of $5 a gallon and not only refused to sell milk for less, but would harass the stores that sold for $4, threw things at them and waved signs and sticks at anyone who tried to deliver their goods? That would be scandalously illegal and the outrage would be on the front page of every paper. Yet, this is the very same principle which is ignored in the case of striking workers, because when a the perpetrator has less money than the victim, that is somehow acceptable. This is why, at best, labor unions and their tactics should be reserved for only the most serious cases and life or death issues. In no case are things like "closed shop" laws acceptable.