The article analyses a letter from the Grand Duchy Chancellery of Sigismund Augustus to the archimandrite of Zhydychyn in Volyn, father Jonah, dated February 20, 1567, which is published in the appendix. The document is a piece of administrative documentation on behalf of the sovereign of the Grand Duchy of Lithuania, informing about the decision of the Goroden General Diet on mobilization of the armed forces and taxation in the Livonian War with the Muscovites (1558–1583).