Seems like they could do whatever they want(?), but a paid ad from PJ Media says:
NOT ALL GOLD IS CREATED EQUAL
PRE-1933 GOLD
PRIVATE
LONG-TERM STABLE GROWTH
NON-REPORTABLE
UNLIKELY TO BE CONFISCATED
VALUED BY WEIGHT, CONDITION, & POPULATION
GOLD BULLION
LACK OF PRIVACY
SHORT-TERM, SOMETIMES VIOLENT FLUCTUATIONS
REPORTABLE
LIKELY TO BE CONFISCATED
RELIES ON SPOT PRICE ALONE TO ESTABLISH VALUE
http://www.startwithgold.com/resources/pjmedia/pjmedia-20120123-0394.php