The Christian Science Monitor explains the case…
Under scrutiny is the Copyright Act’s 1908 “first sale” doctrine, which provides that after a copyrighted good (like a book or CD) has been sold once, it can be resold for profit without the authorization of the copyright owner. At the crux of the matter (and what the Court is ruling on) is whether the “first sale” doctrine applies to any copyrighted work, regardless of where it was manufactured, or only those manufactured in the US.
If it rules that the “first sale” doctrine only applies to copyrighted goods manufactured in the US, it could render illegal the sale of used books, media, art, and other copyrighted works produced abroad. Which is why interested parties, from the Association of American Publishers to Goodwill to eBay, Powell’s Books, and the American Library Association are watching the case closely.
Where’d the case come from? A college student found he could get Thailand-made editions of textbooks shipped to him cheaper than buying in California, and began reselling them for a profit online.