What is the difference between official and unofficial industrial action?

Industrial action that is authorised or endorsed by a union is official. Those able to authorise or endorse industrial action are: a person empowered by the union rules to do, authorise or endorse acts of the kind in question; the Executive Committee, President or General Secretary; any other committee of the union and any other official whether or not employed by the union. If the union then repudiates the action, it becomes unofficial.