Unions can sometimes prevent an employer from firing a bad employee. Other times, they can get in the way of getting work done by saying "It's not their job", even when the employee was perfectly willing to do it.
I ran into this (on a very minor scale) while working at a grocery store part time during my early community college days. The store was unionized, but there were at least three different unions, depending on which department of the store you worked in. I ended up in the bakery working evenings, the only one manning the counter there, right across from the deli. There were times when I couldn't run to the restroom all evening because the three deli employees were in a different union and couldn't come over and watch the bakery counter for five minutes.
Unions can also block career paths because of seniority preference, a newer guy won't be considered for promotions even if he is more than capable and has showed dedication if the older one are given preference just by longevity. I'm not against unions in general for blue collar jobs but I do believe that they shouldn't have more power than the company, it's all about balance. I come from a country where the lefty populist government used unions to destroy all the private sector by giving them all the power.
The former is an unavoidable and, considering the benefits, worthwhile outcome of unionization. The latter is to protect bosses from slowly overloading one person/role and using that to increase work for everyone or split the union.
This is not an inherent problem with unions tho
It's an inherent problem with American unions and how they navigate the law.
Where does it say that a union must do those things?
unions are not a panacea ... Where I am from, in some of the states, all manufacturing had to move out because unions kept going on strikes and lockouts. So its not only American unions that are bad, there are bad unions everywhere.
I feel the worker council concept may work better.
>Unions can sometimes prevent an employer from firing a bad employee.
Bad managers routinely do the same thing except they come with none of the upsides of unions.
I've seen lots of complaints and propaganda about unions over the years, but at the end of the day "The only thing worse than a bad union is no union."
There aren't any obvious or inherent problems with unions, unless you are an exploitative employer.