A union organizer (or union organiser in Commonwealth spelling) is a specific type of trade union member (often elected) or an appointed union official.
In some unions, the organizer's role is to recruit groups of workers under the organizing model. In other unions, the organizer's role is largely that of servicing members and enforcing work rules, similar to the role of a shop steward. In some unions, organizers may also take on industrial/legal roles such as making representations before Fair Work Commission, tribunals, or courts.
In North America, a union organizer is a union representative who "organizes" or unionizes non-union companies or worksites. Organizers primarily exist to assist non-union workers in forming chapters of locals, usually by leading them in their efforts.