One of the religious communities whose activities were monitored by State Security Service was the Seventh-day Adventist Church, a Protestant denomination which has existed in the territory of Croatia since the beginning of the 20^th century. Besides the problems common to all religious communities, problems in relations between the Seventh-day Adventist Church and the communist regime also arose, for instance, in education, employment and in the army due to absence from school and work on Saturdays on religious grounds. This is illustrated by an internal note by the State Security Administration/Zagreb Department dated May 1955, concerning a complaint from leaders of the Seventh-day Adventist Church to State Internal Affairs Secretariat of the People's Republic of Croatia.               

The reason for the complaint was the initiation of infringement proceedings against 15 Adventist craftsmen, due to the closure of their workshops on Saturdays, filed by the State Security Administration/Zagreb Department. The note moreover reveals information on other State Security Administration activities related to members of the Seventh-day Adventist Church. It mentions the questioning of church members as a part of two investigations against leaders of the District Committee of the Seventh-day Adventist Church in Zagreb. Doubts were also expressed that many church members, in particular craftsmen, were “promoting and distributing” religious publications in their homes and workshops. To halt such practices, the State Security Administration conducted searches of their homes and workshops. Reports on the results of its investigations were sent by the Zagreb Department to the federal and republic State Security Administration, and  to the equivalent services in Bosnia and Herzegovina, Slovenia and Macedonia. The extent to which the State Security Administration monitored the activities of religious communities is also illustrated by the following: in reply to a complaint from leaders of the Seventh-day Adventist Church to the State Internal Affairs Secretariat of the People's Republic of Croatia concerning the State Security Administration's intention to obtain data about the Church’s internal activities and organisation, the Zagreb Department stated that it “has  long been in possession of all, including the minutest details, on the Church’s organisation.”