The paper presents a letter from Baron Engelshofen sent at the end of 1743 to Patriarch Arsenije IV (Jovanović Šakabenta), in which the issue of convening the Serbian National-Ecclesial Congress (1744) is considered. Baron Engelshofen here informed the patriarch about his plein potentiel as an imperial commissioner at the assembly, depicted the basis for convening the assembly and asked the patriarch to determine the exact date and number and names of the deputies (deputations) at the assembly. In historiography, the Congress of 1744 was accepted as one of the most important, because it also confirmed the Serbian Privileges by Maria Theresa and their translation into Serbian (i.e., Slavo-Serbian). Therefore, the authors believe that the attached document expands the knowledge about the functioning of Serbian privileged issues in the Habsburg Monarchy during the 18th century. After the Second Migration and the Peace of Belgrade (1739), the question of the status of the Serbian people was addressed. Also, the War for the Austrian Succession (1740-1748) in the first phase brought into question the survival of the Habsburg Monarchy, which brought relations within the state to a new level. Mostly to quell the dissatisfaction of the Serbian people due to the legal article 46/1741 Dieta Posonienssis, which prescribed that only Roman Catholics in Croatia and Slavonia have the right to immovable property, as well as legal article 18/1741, which required the development of Tissa and Moris Frontier and the inclusion of their territories in the Hungarian county system, at the request of the Serb National Deputation. Maria Theresa confirmed the Privileges on April 24, 1740 through the Austrian Court Chancellery and on May 18, 1743 through the Hungarian Court Chancellery declaring them military authorities on August 4, 1743.