The Code of Indian Offenses
The Code drove many ceremonies underground and is one reason so much Native American religious practice is guarded from outsiders, alongside older traditions of restricted sacred knowledge. The rules were not formally lifted until a January 1934 directive, over fifty years during which practising openly was itself a punishable act.
Interior Department Code of Indian Offenses (1883, revised 1892); John Collier's Circular 2970 (January 1934), lifting the ban
US federal rules issued in 1883 that made Native American religious ceremonies, including the Sun Dance, punishable offences.