Coming from someone that has been a member of two trade unions, one by my own choice and the other because it was mandatory to join it where I worked, I can say that the unions I have been witness to first-hand are working only in the interest of the union bosses.
I joined an independent truckers union in hopes of being able to find freight that actually payed to haul it. A lot of drivers near me joined this same union because the scale of freight had dropped to an absurdly low price (another great injustice we had the Teamsters up north to thank for).
What ended up happening was that the union bullied all local businesses into boycotting any union hauling and dropped their rates even lower until only the most desperate of all drivers would truck it. Basically my union sat around getting fat from the dues it was receiving while all of the drivers sat empty for weeks at a time. There were even snipers shooting "scab" truckers who dared to try and feed their families while the fat union bosses dined in fancy restaurants and putted around town with their Bentleys.
Long story short, like most truckers Unions, it imploded. While we sat around waiting for wages that approached livable, other truckers went broke doing "charity" hauls. Companies big and small started contracting from national non-union based firms that gladly hauled their freight at a cheap rate, so long as there was a lot of freight to haul. They payed their company drivers .20 cents a mile to move it and we waited around with our thumbs up our duffs.
This is not an isolated incident, this could be said of unions in general. There arises a need for a union when wages or work conditions require it. Union gets what it wants, then it wants more, until there's nothing left to take. Shut down greedy organized crooked labor unions, and give the working man something to live on.
You know, there's a reason they still haven't found Jimmy Hoffa.