There was a Treasury decision in 1971 that affirmed this, however, when one files FOIA Requests looking for clarification, the cite some Supreme Court decision from the 60s that says something like you are a slave now shut up. Or something to that effect, I can't remember. But I definitely have it saved.
Printed copy · Anthology Volume 7, page 827Printed copy from The Tender For Law Anthology, Volume 7, page 827 (printed 13 June 2014). Added by this site; not part of the Facebook export.