The IWW is more than a simple federation of Industrial Unions. All are members of, and participate directly in the mass organization. Within this One Big Union, workers are grouped according to the affinity which arises from having a common industry and common workplace. In all cases the dividing lines are based on what is most practical. Members can transfer freely from one IU to another when they change jobs.
Many people work in more than one industry at the same time.
The Industrial Union is free to make its own decisions and bylaws, provided they do not violate the IWW constitution. IU 120 Forestry Workers logging, lumber milling, harvesting of bark, sap, forest herbs and plant products, trapping and hunting, arboriculture, silviculture, foresters and forest stewards.