Look at 16 CFR 256 and 39 USC 3009.

This will give information on what you can and can't do in the
area of shipping materials which are not ordered.

I don't recall the original question, but one thing I would
consider is that it is possible to have inadvertently ordered
something (perhaps on a former invoice there was a box which
said something like "check here if you do not want supplemental
material", or perhaps somewhere along the line there was a
letter of inquiry or a phone call that got misinterpreted).

In any case, it seems to me that publishers are usually willing to
cooperate when asked to take something back.

Jim Mumm
Acquisitions / Serials Librarian
Marquette University Law Library
9724mummj@vms.csd.mu.edu