USPS reminds postal employees not to cross out barcode as mail moves through the system
The Intelligent Mail® barcode contains important data that is used to provide mailers — including the Census Bureau — with information, such as when the mailing entered the mailstream and undeliverable or address correction information. But technology cannot reliably produce this information if it can’t read the barcode.
That’s why the Postal Service™ is telling employees to make sure they don’t obliterate the barcode as mail moves through the system. Specifically, employees should not mark through, obliterate, or affix any labels over the Intelligent Mail barcode.
Also, the Postal Service wants to make sure that when employees mark up First-Class Mail® items, they use only clear space on the front of the envelope, being careful not to mark over any address or barcode information.
source: Postal Bulletin