The newly formed FIA expanded its representation to Queensland and South Australia in the following year at its first full conference held in Melbourne in April 1909.

Half the union's membership was from New South Wales, which was divided up into several branches, including Sydney, Lithgow, Newcastle and Granville.

[2] The FIA became increasingly militant during the first two decades of its existence, influenced by the debate over conscription in World War I, to which it was opposed, and the Australian General Strike of 1917, which involved 3000 New South Wales ironworkers.

Following the recovery of the economy in the late 1930s the position was made full-time and Thornton moved to Sydney, where he strengthened communist influence within the FIA.

[3] Thornton's leadership of the FIA was threatened in the 1949 union elections when the Balmain branch, backed by the Labor Industrial Groups, ran a rival ticket headed by Laurie Short.