Between 1935 and 1937 Melita Norwood did little to hide her leftwing views and she became a trade union organizer for the women's clerical trade union, the Association of Women Clerks and Secretaries (AWCS) at BN-FMRA. She had been recruited to the AWCS by her aunt, Margaret Stedman, the first wife of Melita's uncle Thomas, who had been Wilfrid Scawen Blunt's solicitor before the First World War.

The AWCS was a left-leaning trade union led by Anne Godwin, and Melita was well known for her militancy. At the 1934 and 1935 AWCS annual congresses she moved resolutions calling on the union to affiliate to the British anti-war movement and the women's branch of Wilhelm Münzenberg's World Committee against War and Fascism. On the first occasion she made her views on the leaking of classified information quite clear, calling on delegates to ‘decide their loyalty to employers and their loyalty to humanity, and to be sure and make public war information that came their way in the course of their employment’. Her resolution was strongly opposed by Anne Godwin, who rejected it ‘on the grounds that the Anti-War Movement was not a Peace Organisation’ but a revolutionary organization that ‘had as one of its objects the overthrow of Governments’. Nevertheless, anti-war sentiment ran high among the delegates, and after Melita had replied to Anne Godwin a vote was taken, resulting in a thirteen–thirteen split, which meant the resolution was not carried. The following year Letty Norwood tried again, presenting the resolution:

The resolution was carried by thirteen votes to one, a personal triumph for Melita Norwood but a cause for concern in certain circles. Despite Andrew Rothstein's exhortations that she was to refrain from open communist and trade union activity, Melita had clearly not done so. Following Hitler's rise to power in Germany, and the shift in communist strategy to counter the fascist threat, her openly anti-fascist activities began to worry those responsible for the agent networks in London.