Black Friday, in British labour history, refers to 15 April 1921, when the leaders of transport and rail unions announced a decision not to call for strike action in support of the miners.
[4] In the 1890s and the first two decades of the 20th century, increasing efforts were made to bring about amalgamations of small, local trade unions and to forge links between different organisations, with a view to securing united action.
In the aftermath of the First World War, the Triple Alliance and united action in general were regarded by many trade unionists as a defence against the threat of wage reductions occasioned by the onset of economic depression.
In Glasgow, for example, the Scottish Union of Dock Labourers broke with the policy of the Transport Workers' Federation and called its members out on strike on 7 May.
Transport and rail leaders were widely criticised for their actions, with J. H. Thomas of the NUR and Robert Williams of the NTWF being singled out for particular criticism.