25 U.S.C. § 1917 : US Code - Section 1917: Tribal affiliation information and other information for protection of rights from tribal relationship; application of subject of adoptive placement; disclosure by court

      Upon application by an Indian individual who has reached the age
    of eighteen and who was the subject of an adoptive placement, the
    court which entered the final decree shall inform such individual
    of the tribal affiliation, if any, of the individual's biological
    parents and provide such other information as may be necessary to
    protect any rights flowing from the individual's tribal
    relationship.