This report deals with the significance of the principle of proportionality in the strike law of Germany and the EU. As far as German law is concerned, the legal basis and content of the principle of proportionality will first be outlined, and then the importance of the principle for labour law in general. The main issue, however, is the role played by the principle of proportionality in industrial action law. There the Federal Labour Court has meanwhile raised the principle to the central yardstick for the assessment of industrial action measures. The relevant decisions will be presented, but also the considerable criticism of these will not be concealed. Subsequently, EU law will come to the fore, whereby the legal basis, the content and the scope of application of the principle of proportionality will be dealt first. On that basis, the application of the principle in industrial action law will be examined. In that context, the focus will be in the decisions of the European Court of Justice in the cases Laval and Viking. The following section is then devoted to the comparison of German and European law. The author here demonstrates that there are considerable differences in the application of the principle of proportionality.