The paper is about the participation of the Constitutional Work Club (CWC) in the debates of the Legislative Sejm over denominational regulations of the parliamentary project of Constitution in years 1919–1921. The role of the main speaker of this parliamentary club on those topics was monopolized by Alfred Halban. He presented a conservative vision of the relations between the Catholic Church and the state, especially he wanted to preserve the ecclesiastical autonomy in its spiritual mission. Simultaneously, he supported the idea of signing the concordat between Poland and the Holy See, because he considered this type of the agreement as a natural consequence of the organizational structure of the Catholic Church. The participation of CWC in the parliamentary debate did not affect the shape of denominational regulations in the Constitution. Nevertheless, this activity had a positive impact because A. Halban was a significant proponent of substantive and meticulous parliamentary discussion on the denominational issues.