Arbitration means that you don't get to sue in real court, but instead you are forced to go through "arbitration", which is a private company hired by your employer that's supposed to make fair decisions in disputes between the party that brings them continued business, and the random person that will never talk to them if they weren't forced to.

This is where organized work forces (most commonly labor unions) show their worth. It's common practice that if you are represented by a labor union, the arbitrator (private judge) is mutually agreed upon by the union and corporation, which helps mitigate massive bias in either direction. Most US companies that mandate arbitration, the employees have zero voice in selecting the arbitrator.