What is a "membership discount" (assuming you don't mean coupons) in the context of a grocery store? Can you give an example of a major grocery store that has one?
For what it's worth,
> The bill clarifies that certain practices, such as promotional pricing, loyalty programs, or price differences based on objective costs like shipping, are not considered prohibited dynamic pricing.
Harris Teeter is an example of a large chain that has promotions (not coupons) that are applied at checkout only if you have your VIC card (their free membership program). There’s a lot of BOGO, a few dollars off etc offers that are tagged to the price label throughout the store.
In Europe every big chain of stores has loyalty programs and they are busy throwing coupons and discounts. And I don't think they are under any obligation to make sure that they offer the same coupons to everyone.
Safeway/king soopers/albertsons all have members only lower prices or membership-only benefits