Rapid changes caused by the COVID-19 pandemic have brought many challenges to organisations worldwide. Trade unions as non-governmental organisations have also adapted to the new situation, therefore, it is essential to clarify how these changes have affected trade union work performance. This article presents a review and analysis of the theoretical guidelines for trade union effectiveness. The aim of the research is to theoretically justify the effectiveness of trade unions and to empirically clarify Latvian trade union leaders’ opinion on providing Latvian trade union effectiveness in the circumstances caused by the COVID-19 pandemic. Within the article, the period of the COVID-19 pandemic is considered as the period between March 2020 and April 2022. The paper theoretically describes a brief description of trade unions as organisations and provides effectiveness dimensions: criteria, indicators and types, established by several authors. Methods applied in the research: theoretical research method: content analysis of management science literature. Empirical research method: a questionnaire method in the form of a structured interview with Latvian trade union leaders. In order to find out the effectiveness of Latvian trade unions, 12 Latvian branch trade union leaders were interviewed in May, 2022.The main results of the study show that, in the opinion of Latvian trade union leaders, the COVID-19 pandemic has not significantly affected Latvian trade union effectiveness. The most difficult aspects during the COVID-19 pandemic as mentioned by branch trade union leaders were the organisation of remote work and on-site meetings, stress, emotional distress problems, hearing complaints about legal norms and attitude of employers towards unvaccinated workers.