Post office fee employment question.

Hey, curious potential employee here to take a moment and question something at the place I was looking at having a job, There's something the clerk does for local houses without mailboxes that involves giving PO Boxes their addressed mail by looking at it through the system but they've started giving out a fee for this of 19$, Is this legal? If it were Illegal or a misrepresentation is there a legal cite to be able to preface to her about it by reference code? I havent been able to find it myself but it does feel like a moral abstraction and not something that is backed by the usps system. THANK YOU FOR ANY AND ALL FEEDBACK <3