This postgraduate specialist work was conducted to demonstrate a comprehensive systematicanalytical approach to the strategy of outsourcing in the public sector with particular emphasis on the need to incorporate trade unionism in terms of responses to the strategy of outsourcing. In addition to introductory remarks theoretical approach to consider trade unionism and its impact on the success of the rationalization of the public sector was processed. The overall view of trade unionism and trade union action strategy is an attempt to ensure the substrate change management paradigm in the direction of greater interest to the needs and problems of employees and real incentive for rethinking the role and importance of trade unions in contemporary society, emphasized compromise and agreement on the key issues of social and economic policy. It emphasizes the status and activities of the public sector in transition countries, which is marked by pronounced deficiencies and significant limitations. Looking for a link trade unionism and the public sector stands out as the basic premise of the measures of the public sector is not its size but efficiency and effectiveness. This refers to the strategic activities in areas that produce the highest quality and value, while other activities aside and outsourced specialized partners, which is recognized as the concept of outsourcing. The outsourcing is one of the strategic options that are nowadays often used in the public sector. A key basis for deciding on the outsourcing is the analysis of financial and economic feasibility of the implementation of the outsourcing. Empirically, the separation of business processes shows that besides the reduction of costs, a substantial increase in the ability and capacity of the system, as a result of increased focus on the core business systems, among other things, could be present. The analytical part of the paper discusses the findings of previous comparative analysis in terms of costs and benefits of public services. In the continuation, a case study is presented with the aim of attempting to find a final solution regarding the outsourcing of the Croatian public sector.