On August 16, 1925, sixteen left-wing groups met, and agreed to form a unified proletarian political party which would include every labour organization with a membership exceeding 100.
[2] The Platform and Bylaws Research Committee of the Proletarian Party Preparatory Council held its first meeting in September 1925.
Two drafts had been authored by rightwing moderates whilst the third (presented by Sano Fumio) represented the communist line.
Sano's draft, which emphasized that the party should be built on class struggle and not reformism, was adopted by the Committee.
[2] However, just two hours after the founding meeting had concluded the leadership elected at the party conference were summoned at the Metropolitan Police Board.