On 6 July 1950 Australian Prime Minister Robert Menzies issued a Directive titled the Charter of the Australian Security Intelligence Organization. The charter was an expanded and more specific form of the 1949 Directive for the Establishment and Maintenance of a Security Service issued by Ben Chifley.
Note the spelling 'organization' used in the Directive. The official title of ASIO was amended by legislation in 1999 to remove this spelling and apply the Australian standard spelling of 'organisation.'
Expansion and revision
Both the Establishment and Charter Directives have been now largely superseded by federal legislation, notably by the Australian Security Intelligence Organisation Act 1979.
References
Charter of the Australian Security Intelligence Organsisation Wikipedia(Text) CC BY-SA