Final answer:
A wildcat strike is the term used to describe a strike that occurs in violation of a no-strike clause and is often unauthorized by union leadership. It usually arises from workers' grievances that are not being addressed satisfactorily within usual union proceedings.
Step-by-step explanation:
The type of strike which occurs in violation of an existing no-strike clause in a labor agreement and often without the approval of union officials is called a wildcat strike. This kind of strike is typically unauthorized by the union's leadership and may occur spontaneously among a group of workers. It represents a direct action undertaken by workers despite any agreements that might exist between the union and the management that would normally prevent such an action. These strikes often occur due to grievances that workers feel are not being adequately addressed through regular union channels or collective bargaining practices.
Historically, the labor movement in the U.S. went through many changes due to industrialization. The Wagner Act was instrumental in establishing the rights of workers to organize and to strike. During difficult times, especially during the postwar era and the Great Depression, workers had to navigate complex legal landscapes and risked much to form unions and to negotiate better working conditions and wages, often through collective actions like strikes. Sit-down strikes and other forms of labor protests played a significant role in shaping labor laws.