In the early 1920s, he was a member of a Freemason’s Lodge “Tomasz Zan”, and in April 1925, after abandoning Polish People's Party "Wyzwolenie", he co-created the so-called "Parliamentary Labour Club" ("Klub Pracy", later renamed into "Labour Party"), together with Kazimierz Bartel. Zyndram-Kościałkowski did not play any significant role in the 1926 May Coup. As key member of the Labour Party, he supported the Sanacja movement, and in May 1927 became a member of the Warsaw City Council. At the same time, he was a deputy chairman of the Association of Army Reservists, and leading member of Association of Polish Cities. In the Parliament, he was responsible for the budget of the Ministry of Military Affairs for the year 1927/28.