An individual employee has little influence over what happens at the workplace and is subject to the arbitrary decisions of his or her employer. Although there are labour laws governing such things as minimum wages, holidays and overtime, these laws establish only minimum rights at a very basic level.
Belonging to a Union and being represented by a Union gives you rights that you do not have as an individual. Rather than dealing with your employer individually concerning the terms and conditions of your employment, employees bargain collectively as a group with the assistance of a Union business representative. The employer is legally obligated to negotiate with your Union and cannot refuse to discuss the issues which are of concern to employees.