The Third Division Telegraphists' and Postal Clerks' Union reregistered as the Union of Postal Clerks and Telegraphists in 1966 with the Fourth Division Postmasters, Postal Workers and Telegraphists' Union merging with it, effective from 19 February 1967. The Third and Fourth Divisions refer to the clerical and lowest-paid divisions of the Commonwealth Public Service respectively. By 1990 the Union had merged into the Australian Postal and Telecommunications' Union.

The Australian Third Division Telegraphists' and Postal Clerks' Union had its origins in the Australian Telegraphists' Union formed in 1920 as a breakaway group of the Australian Commonwealth Post and Telegraph Officers' Association. It deregistered just a few months later but was formed again in 1921 under the same title. By 1925 it was known as the Australian Telegraphists' and Clerical Assistants' Union. Two years later, in 1927, the Union re-emerged as the Australian Third Division Telegraphists' and Postal Clerks' Union, the term 'Third Division' referring to the clerical division of the Commonwealth Public Service. Operating until 1966, the Third Division Telegraphists' and Postal Clerks' Union reregistered as the Union of Postal Clerks and Telegraphists and the Fourth Division Postmasters, Postal Clerks and Telegraphists' Union merged with it, effective from 19 February 1967.