What does "industrial action short of a strike" mean?

An example of "industrial action short of a strike" is when workers refuse to perform overtime. Industrial action can take the form of a strike, action short of a strike or a lock-out. A lock-out occurs when the employer does not allow workers to work during a dispute.

Industrial action is official if it is supported by a trade union and the members of the union are involved in it. Industrial action is protected by law when the dispute relates to a business-related disagreement between workers and the employer, a secret ballot is held and supports the action and detailed notice of the action is given to the employer at least a week in advance.