Abstract   The overall aim of this paper is to examine the impact of ideologies and norms on a legal system. Against a background of a description of the hierarchy of norms in Swedish labour law and in European Union law, respectively, the paper aims to specifically demonstrate the problems caused by the different hierarchies of norms when implementing EU directives in Swedish labor law.   The research question examines how the trade unions’ right to industrial action towards an undertaker providing transnational services by posting of workers, is affected by the implementation of the Directive 96/71/EC of the European Parliament and of the Council of 16 December 1996 concerning the posting of workers in the framework of the provision of services. The paper answers the question under what conditions the Swedish trade unions have the right to take industrial action in situations of posting of workers.   Through the study of sources of law and adhering to traditional jurisprudence, this paper investigates the legislation regarding trade unions’ rights to take industrial action in situations of posting of workers.   In addition to the jurisprudential research, a glance at the history of ideologies is provided. The purpose of this is to explain the role of ideologies in the origins and history of Swedish labour law, as well as their role in the current development of law. With the ideological and historical discussion as a background, this paper investigates Swedish law and EU law using a comparative approach. The purpose is to illustrate how differences in ideological bases are determinant of differences in current legislation and legal practice.   The paper studies the development of law since the 1990s with regards to the right to industrial action in situations of posting of workers. The Swedish labour law has been revised since Sweden joined the European Union. The presentation looks particularly at the following cases in the Swedish Labour Court: AD 1989 No. 120 (the Britannia case) and AD 2005 No. 49 (the Vaxholm case). The paper studies the Posting of Workers Directive and presents an analysis of the European Court of Justice Case C-341/05 Laval un Partneri Ltd (the Laval case). To allow for analysis and a broad discussion on the implementation of the Posting of Workers Directive, an account is made of the different government committee instructions, committee of inquiry reports, and governmental legislative proposals of importance for the implementation of the directive into the Foreign Posting of Employees Act, and for the legislative changes prompted by the Laval case (i.e. the lex Laval).   The main conclusion drawn from the study of the legislative development is that the level of legislation of the Swedish labour market will increase due to the tendency of europeanisation. The study also establishes the importance of ideologies, norms and values for the development of a legal system. This paper does not fully answer whether the set of norms on which Swedish labour law is based is about to change, but the trend is that on the whole no such changes have been observed. The existence of lex Laval has not affected the basic set of norms of Swedish labour law.