The chain is going to try to enforce the law on wearing masks indoors in public places in all its stores.
Good! This should have been the case from day one in all shops over a certain size regardless of the efficacy of masks. The rule should be very simple and be enforced: no mask = no entry or no service.
There should be very few exemptions, certainly no self-certifications, and everyone not masked up must be allowed to be challenged and provide official proof. That will require another change in the law or be temporarily allowed under the special powers now in place, but so be it.
I know there are some genuine cases, but I don't think they are in the numbers claimed today. Also, if your breathing is so compromised by wearing a mask, you should probably be avoiding places where the virus can be active on trolleys, baskets, tills and their conveyors, and even on products picked up and put back by other shoppers.
Then think of the other mask bonuses. Nobody can tell if you are ugly when you are wearing a mask; and you can leave your teeth in a glass on the dressing table when you go out - double bonus!