> no one
I recently took a union software job after I was laid off due to the CEO having a tummy ache one morning. Many of my new co-workers were explicitly interested in the company _because_ there was a union.
It's very imperfect but such is life. It's all new to me but here's what I've seen so far:
a) Employees have a voice. That doesn't mean that management is forced to do anything, but at least it's possible to be vocally opposed to eating a shit sandwich.
b) We are protected by a contract. If you are called into a police station, you ask for a lawyer for protection according to the law. If an employee finds themselves in an adverse meeting/situation with management, they can call in a steward to protect them according to the contract.
c) The union is us, the workers. We self-organize. It simply gives us a structural framework to work within. An entity for my employer to recognize. It's not ran by an authoritarian who waves a magic wand to make things happen.
That's it. There seems to be this weird idea that I can screw around for 40 hours a week and have the union protect my job. The union told us that we very much still have to do our jobs (duh).
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To go on a little side tangent. Some countries, such as Finland or Norway, have no minimum wage because unions are (a) everywhere and (b) (allowed to be) powerful enough to protect workers. Honestly it's the best of both worlds. Less government intervention but at the same time workers hugely benefit from collectivization. They don't need to beg their politicians to raise wages - they do it themselves because they are given the power to do so. In the US, we instead rely on the lizards in DC to protect our wages because unions have been so stripped of power.