The linked story is obviously written from a union organiser point of view.
When I worked in retail, the union which I was forced to join did nothing for their members other than collect dues. Because of the over-supply of low-skilled people willing to work for minimum wage (which certainly included me at the time), our union rep had little bargaining power. People were hired and fired without any union involvement that I’m aware of.
Many retail positions require little training, so there’s little cost to the companies to bring in new employees.