The Free Trade Unions (, SSS) was a central trade union organization in Bulgaria. SSS was founded in August 1904, and was politically tied to the Bulgarian Social Democratic Workers Party (Obedinena).Kowalski, Werner. Geschichte der sozialistischen arbeiter-internationale: 1923 - 19. Berlin: Dt. Verl. d. Wissenschaften, 1985. p. 288 As of 1904, SSS had 1,188 members. By 1907 the membership had risen to 1,884.Linden, Marcel van der, and Jürgen Rojahn. The Formation of Labour Movements, 1870-1914: An International Perspective. Contributions to the history of labour and society, v. 2. Leiden: E.J. Brill, 1990. p. 410
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