Are you talking about public employee unions or trade unions?
All unions -- every last one of them -- are evil to the core.
Their very existence is predicated upon class envy and stems from a history intertwined with international Communism. Liberty and unions are fundamentally at odds.
One of the more joyous events in my long lifetime was busting a long-entrenched union and then watching the featherbedding "workers", some of whom had worked at the facility for three decades, get fired. These lazy, unproductive lowlifes with their precious seniority no longer had the protection of the local union goons and were rightly dismissed. The company then became much more prosperous since the deadwood was eliminated along with the archaic workrules imposed by the union thugs. And we anti-union employees who remained after the long-overdue downsizing were amply rewarded in that prosperity.