I thought there were already laws to prevent this but this is good to see. It should also shine light on Amazon's practices which forced this on USPS. I cancelled my Amazon Prime account several years ago and checked he no "Sunday" delivery option in my account, and with less orders and that option and not ordering when I know it could possibly still deliver through USPS ignoring the Amazon preference, it hasn't happened.
https://disrn.com/news/pennsylvania-christian-sues-us-postal-service-over-mandatory-work-on-sundays
https://disrn.com/news/pennsylvania-christian-sues-us-postal-service-over-mandatory-work-on-sundays