A more thorough explanation:

The American Federation of Labor and Congress of Industrial Organizations (AFL-CIO) is a group of more than 100 labor unions that work together to improve the lives of workers in the United States. Each union operates independently, but they benefit from the AFL-CIO's political activities and policies for the national labor movement.

For example, if a worker is part of a union that is part of the AFL-CIO, they may have access to better benefits and protections because the AFL-CIO has negotiated with employers on behalf of all its member unions. Additionally, the AFL-CIO may lobby the government to pass laws that benefit workers, such as minimum wage increases or better workplace safety regulations.