Not necessarily.
Grocery store workers in the majority of the US are not unionized (they are in California I believe), but that doesn't necessarily reflect bad working conditions (at least in relation to the US). [Yes, I realize NK is NOT a grocer, this is an example of retail work in the US]
IT CAN reflect what their target employees are in some cases (younger individuals or those looking for additional income in some places, others have varying pay depending on the position with some positions specfically focused for some of those types of employees with the expectations those positions will not really buy the healthcare or other items).
Some of it may be part time work where the default is expected that one can schedule times to not work if they wish and don't have to go in as much so the company feels they don't need the days off like a full-time worker.
With that said, most grocery stores probably would also flat out refuse to recognize a union in the United States, especially if they feel that union is trying to demand things that are not useful to the business (for example, trying to force the above part time workers to be given 2 weeks vacation fully paid, getting a healthcare plan that is affordable for those part time workers to afford on part time pay, and paying filler positions high wages).
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