The rules for media mail do change as the years go by. Sometimes clerks are not aware of the subtle changes (seriously, with apologies to the writers, the DMM is not the most enjoyable reading). Likewise, there is a lot of misinformation out there among consumers as well.
People also get confused between Media Mail and Library Mail, which are similar but not the same.
Always go by the
current rules. The relevant section of the DMM (Section 173) is available online at
http://pe.usps.com/text/dmm300/173.htm. Disregard all references to DMM 173.3.2 that are often cited (even on the USPS website), because that is from the old version and that subsection no longer exists!
In a nutshell, YES YOU MAY include an invoice in Media Mail without additional charge other than weight. This is the relevant section:
Quote:
6.0 Enclosures and Attachments for both Media Mail and Library Mail
6.3 Invoice
An invoice, whether it also serves as a bill, may be placed either inside a Media Mail or Library Mail piece or in an envelope marked "Invoice Enclosed" and attached to the outside of the piece if the invoice relates solely to the matter with which it is mailed. The invoice may show this information:
a. Names and addresses of the sender and addressee.
b. Names and quantities of the articles enclosed, descriptions of each (e.g., price, tax, style, stock number, size, and quality, and, if defective, nature of defects).
c. Order or file number, date of order, date and manner of shipment, shipping weight, postage paid, and initials or name of packer or checker.
The confusion some people/clerks have is with Section 6.4 regarding enclosure/attachment of Incidental First Class Mail:
Quote:
6.4 Incidental First-Class Mail Attachments and Enclosures
Incidental First-Class Mail matter may be enclosed in or attached to any Media Mail or Library Mail piece without payment of First-Class Mail postage. An incidental First-Class Mail attachment or enclosure must be matter that, if mailed separately, would require First-Class Mail postage, is closely associated with but secondary to the host piece, and is prepared so as not to interfere with postal processing. An incidental First-Class Mail attachment or enclosure may be a bill for the product or publication, a statement of account for past products or publications, or a personal message or greeting included with a product, publication, or parcel. Postage at the Media Mail or Library Mail price for the host piece is based on the combined weight of the host piece and the incidental First-Class Mail attachment or enclosure.
Incidental First Class Mail is permitted in Media Mail without having to pay First Class rate. (note the first line in Subsection 173.6.4)
Clerks now often make 2 mistakes based on some older versions of the DMM: 1) mistake invoices for First Class Mail; 2) mistake Incidental First Class mail for First Class Mail.
To add insult to injury, they make the huge mistake of assuming if one part does not qualify, then the entire package does not qualify. There is an exception for Incidental First Class Mail.
Clerks are in error if they make you mail the entire package as Parcel Post just because you enclosed an invoice (Media Mail eligible) or non-Incidental First Class Mail (you pay additional First Class rate for
only the unqualified part!). The first line of Subsection 173.6.2 states this very clearly. In the quote below, I have omitted the long list of exceptions that do not require payment)
Quote:
6.2 Written Additions
Markings that have the character of personal correspondence require, with certain exceptions, additional postage at the First-Class Mail prices. The following written additions and enclosures do not require additional First-Class Mail postage:...
So in most cases, if you have non-Incidental First Class Mail enclosed/attached, that basically means tacking on an additional 47¢ (current First Class 1 oz rate).
Sorry about the long post, but there were just too many different misunderstandings to address.