If your boss demands you wear specific clothes, and demands you should keep those clothes clean in your own time, they are effectively making you do more work after hours using tools and utilities that you also have to pay for. It is perfectly reasonable for a union to try to negotiate either: a) laundry pay and utility compensation, or b) for the company to do this work instead. In this case the union is demanding the latter.
Another variable for me would be how many company provided outfits there are. If they just give them one apron and expect it to be washed daily, that would fall under an onerous requirement in my opinion and would justify a laundry service.
When comparing it to the company provided footwear, their example was a woman who went through three sets of shoes and being told three different times the shoes weren’t suitable for arbitrary reasons. If they are going to be that picky, they should absolutely foot the bill to ensure the uniform fits their standards.