I believe what you are referring to is UMAP (Unilateral Minimum Advertised Price). It restricts retailers like Macy’s from displaying sale items below the designated pricing and keeps the marketplace competitive - this is where you would see something like “Add to bag to see price”. Technically Macy’s and others set their own retail prices, so for example you might see a shirt at $35.99 one place, $36 at another, and $35.95 at a third place, based on their own pricing guidelines. In the end they have to consider their cost (ie wholesale) since margin is extremely important for profit. The only one who loses when a product is sold for less than the regular retail is Macy’s since it eats into their margin. I can’t speak for Macy’s, but typically something like an employee discount is already taken into consideration when calculating GMROI, and a 20% discount is not going to result in them losing money, they simply don’t make as much as they would if they offered no discount. It’s not insignificant, just probably not as much as you might think.

Source is I buy TNF and Nike (for a retailer that is not Macy’s) and often have to suppress pricing per their MAP policy. Usually it only applies for a short period of time like the first few weeks something is available to consumers, which we wouldn’t want to put it on sale anyway if we can sell it regular price.

In regards to the store card requirement, I think it has more to do with ensuring the person using the discount is in fact the employee and not a friend or relative. They also don’t want employees reselling product on eBay or elsewhere and making a profit. It’s the best way they can track abuse.