Industrial action can still be found unlawful by the courts if, taking all the circumstances of the case into account, that action has a disproportionate effect on the rights and freedoms of third parties, or general interests such as public health or safety. In determining whether a strike or other form of industrial action should be prohibited on that basis, the courts may still take into account whether the action has been called for as a last resort and whether it has been pre-announced. However, these two aspects are from now on only to be seen as relevant factors that should be taken into account together with all the other aspects of the case, instead of formal requirements that have to be met in order for industrial action to be lawful at all.
The Supreme Court based its ruling on the European Social Charter. This is the second time in a short period that the right to strike has been stretched. In October 2014, the Supreme Court ruled that unions are also allowed to call employees of clients or suppliers out on strike in order to put pressure on their employer. Traditionally, trade unions were only allowed to organise a strike in companies when they had a conflict with that company.