This article examines the legal challenges regarding the interpretation of the applicable national legislation on military operations in Ukraine, as well as the legal concerns and discrepancies regarding the classification of the activity of private military and security companies in international armed conflicts or internal tensions. An important element of this article is the analysis of the previous Alexander Alexandrov and Yevgeny Yerofeyev in 2016 both for the entire Ukrainian judiciary in general and for the prosecution of foreign nationals who are directly involved in hostilities in particular.