In 1934, it joined the Finnish Federation of Trade Unions (SAK).
[3][4] In 1938, Niilo Wälläri was elected as the union's president, known for his advocacy of industrial action.
Under his leadership the union secured a closed shop for the Finnish Merchant Navy.
The union's membership grew, reaching 6,805 by 1955, but in 1956 it resigned from the SAK.
Three years later, it was a founding affiliate of the rival Finnish Trade Union Federation (SAJ), and since 1969 it has been affiliated to its successor, the Central Organisation of Finnish Trade Unions.