Most unions start with some sort of noble cause of protecting the local labor as companies or businesses might over burden them with less pay. Although such practises of businesses can be overthrown by starting yet another competing business with better value of labor most often or not the labourers resort to collectivism by forming a union and protesting.
Soon these groups decide their own prices as they form the service sector and thus causing price inflation of the services. A individual from a union who wants to provide better service with lower price will be socially outcast and not allowed to practise his skill or in some instances violence is used against that individual.
For example in India, there are unions everywhere from fisherman, to taxi (auto rickshaws), hospitals, bus drivers, teachers, etc.
What is ironic is, these are the same people who complain about the high prices which other unions service charges. Example a fisherman sells at high prices in india and then goes to complain that the hospitals are expensive when fisherman is sick. Fisherman does not introspect that he is part of the problem and instead of correcting himself at his service he blames hospitals for the high charges.
Union members behave like thugs when the customer proves their corrupt practices. Also since there are large members of people in these unions it becomes easy for politicians to bribe the members to cast vote one way or the other thus becoming a corrupt system.
Solution: A simple solution is not to form a union at all. If a certain businesses practising unfairly, the best way to do is to start competing business or learn other skill so that that particular businesses will be indirectly forced to provide better compensation or perish. This way unions are not formed and prices won't be unfair.