Browse Trade Unions - O
- Official Court Interpreters & Translators Professional Association of NSW (1977 - )
- Operative Bakers Society of Victoria (1862 - c. 1914)
- Operative Bakers Union of Victoria (c. 1918 - 1975)
- Operative Bootmakers Union (1879 - ?)
- Operative Bootmakers Union of South Australia (1882? - ?)
- Operative Bricklayers & Rubble Wallers Industrial Union of Workers
- Operative Bricklayers Tilers & Tuckpointers Society of South Australia (1924 - ?)
- Operative Masons & Bricklayers Association, Sturt District (1890 - )
- Operative Masons Benefit Society (1850 - 1851)
- Operative Masons Society of South Australia (1914 - 1918)
- Operative Painters & Decorators of Australasia (1915 - 1918)
- Operative Painters & Decorators Union of Australia (1918 - 1993)
- Operative Painters & Decorators Union of Australia, NSW Branch (1913 - )
- Operative Plasterers & Plaster Workers Federation of Australia (1963 - 1992)
- Operative Plasterers Federation of Australia (1925 - 1963)
- Operative Plasterers Federation of Australia, NSW Bransh
- Operative Plumbers Society of New South Wales
- Operative Sailmakers Society of Sydney, NSW (1886 - )
- Operative Sailmakers Trade Society of New South Wales (1949 - 1976)
- Operative Stonemason Union
- Operative Stonemasons Society of Australia (1919 - 1991)
- Operative Stonemasons Society of New South Wales (? - 1918)
- Optical Employees Union (1942 - )