I can find no evidence that private competitors must legally charge a higher rate than USPS. Do you have a source for that? My understanding was that USPS had to compete directly with private mail carriers.
From Wikipedia: "Regarding the monopoly on delivery of letters, the report notes that the monopoly is not complete, as there is an exception for letters where either the amount paid for private carriage of the letter equals at least six times the current rate for the first ounce of a single-piece First-Class Mail letter (also known as the "base rate" or "base tariff") or the letter weighs at least 12.5 ounces."
Thanks for the link - the 6x in pricing is to enforce the monopoly on delivery of letters rather than all mail items. It only applies to (i) items weighing less than 12.5oz (ii) to the first 1.0oz of a single piece of mail.
Certainly an enforcement of USPS' monopoly on letter delivery, but not a blanket price fixing across all mail items and types.
This subthread is in response to a comment that said:
>" What is the direct competitor for bulk letter delivery? Historically that's not profitable so no private company does it and instead they all focus on the profitable package business, or edge case super-fast high cost delivery. "
So I responded with reasons why there was no competitor for letter delivery:
>" Well, the law currently requires that any competitor charge many times (7x if I recall correctly) more than the USPS for mail, and they are not permitted to use letter-boxes, so it is rather unsurprising that UPS and FedEx charge more for first class mail."
https://en.wikipedia.org/wiki/United_States_Postal_Service#2...
edit: Here is the law https://www.law.cornell.edu/uscode/text/39/601