There’s a law against discriminating against users of the mail

What's fair is fair: Amazon customers get delivery on Sunday, SRO residents get none at all

From the article: "...The Postal Service is going to deliver Amazon packages on Sundays only to customers who live in New York and Los Angeles; eventually the program will encompass a few other big cities like Dallas, Houston, and New Orleans. That seems like it would discriminate against people who live everywhere else, particularly the residents of rural America, who will probably never get Sunday delivery, no matter..."

Article Reference: www.savethepostoffice.com
39 U.S.C. 403(c), law against discriminating against users of the mail,