When a group of employees come together so that they can bargain with their employers, they are said to form a union. Without a union, any employee can be hired and fired by the employer at will, so a single employee does not have any bargaining power with his employer. However, when all the employees of a factory or an enterprise unite together, they can bargain with the owners as equals. This is because the owners cannot fire all the employees at one go. If the owner were to do so, then their enterprise or factory will have to close. And it will be weeks or months before they could hire all the employees again. That is why a union has power, because they can do collective bargaining.
There are unions in Calgary and Canada, which also work on the principle of collective bargaining. These unions bargain with the employers whenever any issue comes up that is relevant to the workers. For example, they can bargain with the employers about the number of sick leave that a worker can take. They can also bargain about the salary of different types of workers in a factory. This is how unions help the workers.