The article presents a document dated 13 February 1903, addressed to the Episcopal Court of the Diocese of Plock by Rev. Infulat Piotr Borniński (1862-1936), Procurator for Finance, Faith and Customs. This is a particularly important document for investigating the origins of the official interest of the authorities of the Plock diocese in the matter of the Mariavites. At the time this letter was written, the Mariavites had already been active for some time (1893) in several dioceses of the Kingdom of Poland. Their work, although perhaps carried out with the knowledge and even general approval of some hierarchs, was not of an official nature.