This is one of my most ambivalent political issues.
Unions have helped physical laborers attain a more equitable compensation for their often life-shortening work and given employees an advocate against managerial abuses.
However, there inefficiencies are a drain on a true free market system and they have had a history of corruption.
There are going to be those who take advantage of workers on the management side to benefit the company, but there are also going to be those who would make a living by profiteering off the dues paid by union members, like so many sycophants.