How did industrial unions differ from craft unions?

In the context of labour law and the history of organized labour, industrial unions and craft unions differ primarily in their membership criteria and organizational philosophy.12

Craft Unions

Craft unions, or trade unions, organize workers based on a specific skill or trade, such as electricians, carpenters, or printers. Their core principle is often summarized by the slogan "one craft, one union". These unions derive their bargaining power from the scarcity of their specialized labour, which they maintain through apprenticeship programs and licensing requirements. Historically, craft unions were the earliest form of organized labour and often excluded unskilled workers.123

Industrial Unions

Industrial unions organize all workers within a particular industry, regardless of their specific skill level. Their philosophy is captured by the slogan "one shop, one union". Unlike craft unions, which rely on the scarcity of a specific skill, industrial unions gain leverage by organizing large numbers of workers, making it difficult for employers to replace them without significant loss of production. This approach allowed industrial unions to successfully represent the semiskilled and unskilled workers in mass-production industries who were often excluded from craft-based organizations.23