The problem with unions

I mentioned unions in another post and I got a few comments asking what is wrong with unions. Theres nothing wrong with workers coming together and bargaining collectively. The problem is when they try to use the power of government to gain special privileges or harm their competition. For example taxi driver unions trying to ban Uber, hotel workers unions have tried to ban Airbnb, trucker unions support laws that make it harder to be an owner-operator trucker, etc