Legal Question in Intellectual Property in Texas

It is good you ask your question, since your question shows you have a misunderstanding of the basics of copyright law.

Copyright is automatic under current law without requirement of any formalities. So the art work you say "isn't copyrighted" probably is copyrighted. Perhaps you mean "isn't registered" when you say "isn't copyrighted." Registration (or application for registration) of the copyright is required as a jurisdictional matter by the Federal District Courts, which have exclusive original jurisdiction in copyright infringement suits since copyrights arise under Federal law, and thus registration is normally required for effective protection of the copyright. Copyright registration is inexpensive and relatively simple. That being said, cafepress apparently assists with unregistered copyrighted material. So, the actual creators apparently just follow the procedures outlined in the page you listed and notify the Intellectual Property Agent of the improper use and cafepress should take steps to stop the infringer from listing such work on cafepress. The Intellectual Property Agent will likely also inform the actual creators that they should register their copyright, and may even require registration (as proof of ownership) before taking action.

Or, are you talking about public domain material when you say "art work that isn't copyrighted"? Public domain material belongs to everyone, including "the person that holds the shop". The creators of public domain material generally have just the same nonexclusive rights as the public.

If you are the creator, and this art work is valuable, then you need to see an Intellectual Property Lawyer like me for advice, so you can try to get back control of your art work.