This article conducts a critical analysis of the issue of the access of military personnel to the legal guarantees of the freedom to associate in trade unions from the perspective of international legal standards. Despite the consistently freedom-oriented evolution of international standards which have become applicable to union freedoms in recent decades, many states still uphold sweeping statutory bans on the unionization of military personnel. The potential engagement of members of the armed forces in any union activity is a contentious issue suspended between the requirement to protect the very essence of the freedom of association (FoA), the practices and traditions established in many states, and the need to maintain the effective security of the state against external threats. The analysis considers the evolution of perspectives presented by competent international supervisory and interpretative bodies which have substantially revised their views in recent years on the extent of necessary legal guarantees and acceptable restrictions on freedom of association with respect to military personnel. The analysis leads to the conclusion that a complete and absolute statutory ban on the unionization of military personnel may be incompatible with current international standards. The absolute requirement to respect the fundamental essence of freedom of association as an unquestionable and universal standard of human rights means that national legislators should guarantee military personnel at least the minimum level of freedom to associate in trade unions.