The purpose of this article is to discuss the procedure of the canonical preliminary investigation in the case of clerics suspected of committing an offence against the Sixth Commandment of the Decalogue with a minor and a person legally equal to him pursuant to Article 1 § 1a of VELM/2023. The Author discusses the various stages of this preliminary investigation, which is of great importance for the possible initiation of a criminal trial. In other words, the thoroughness of this investigation provides a just basis for the competent ecclesiastical superior (hierarch) to take the appropriate legal action. The above topics are discussed on the basis of an analysis of the universal and particularistic legal regulations relating to the Eastern Catholic Churches, with particular reference to the Byzantine-Ukrainian Catholic Church in Poland.