Question: What is the largest labor union in the U.S.?

List of labor unions in the United States

This is a list of labor unions in the United States. Unions exist to represent the interests of workers, who form the membership. Under US labor law, the National Labor Relations Act 1935 is the primary statute which gives US unions rights. The rights of members are governed by the Labor Management Reporting and Disclosure Act 1959. List Below
Largest unions

AFL-CIO
The American Federation of Labor-Congress of Industrial Organizations is the leading confederation of US trade unions.
Air Line Pilots Association
Amalgamated Transit Union
American Federation of Government Employees
American Federation of Musicians
American Federation of School Administrators
American Federation of State, County and Municipal Employees
American Federation of Teachers
American Postal Workers Union
American Train Dispatchers Association
Associated Actors and Artistes of America
Actors' Equity Association
American Guild of Musical Artists
American Guild of Variety Artists
The Guild of Italian American Actors
SAG-AFTRA
Bakery, Confectionery, Tobacco Workers and Grain Millers' International Union
Brotherhood of Railroad Signalmen
California Nurses Association
California School Employees Association
Communications Workers of America
Farm Labor Organizing Committee
Federation of Professional Athletes/National Football League Players Association
Glass, Molders, Pottery, Plastics and Allied Workers International Union
International Alliance of Theatrical Stage Employees
International Association of Bridge, Structural, Ornamental and Reinforcing Iron Workers
International Association of Fire Fighters
International Association of Heat and Frost Insulators and Asbestos Workers
International Association of Machinists and Aerospace Workers
International Brotherhood of Boilermakers, Iron Ship Builders, Blacksmiths, Forgers and Helpers
International Brotherhood of Electrical Workers
International Federation of Professional and Technical Engineers
International Longshoremen's Association
International Plate Printers, Die Stampers and Engravers Union of North America
International Union of Allied Novelty and Production Workers
International Union of Bricklayers and Allied Craftworkers
International Union of Elevator Constructors
International Union of Operating Engineers
International Union of Painters and Allied Trades
International Union of Police Associations
Laborers' International Union of North America
Marine Engineers Beneficial Association
National Football League Players Association
National Air Traffic Controllers Association
National Association of Letter Carriers
National Nurses United
National Taxi Workers' Alliance
Office and Professional Employees International Union
Operative Plasterers' and Cement Masons' International Association
Professional Aviation Safety Specialists
Seafarers International Union of North America
Sheet Metal Workers International Association
Transport Workers Union of America
UNITE HERE
United Association of Journeymen and Apprentices of the Plumbing, Pipefitting and Sprinkler Fitting Industry of the United States and Canada
United Automobile, Aerospace & Agricultural Implement Workers of America International Union
United Food and Commercial Workers
United Mine Workers of America
United Independent Technology Technicians of America
United Steel, Paper and Forestry, Rubber, Manufacturing, Energy, Allied Industrial and Service Workers International Union
United Transportation Union
United Union of Roofers, Waterproofers and Allied Workers
Utility Workers Union of America
Writers Guild of America, East
Change to Win Federation

International Brotherhood of Teamsters
Graphic Communications Conference (GCC)
Service Employees International Union
Workers United
Colorado Workers for Innovations and New Solutions (WINS)
United Farm Workers of America
Independent
Aircraft Mechanics Fraternal Association
Allied Pilots Association
Coalition of Graduate Employee Unions
Directors Guild of America
Dramatists Guild of America
Fraternal Order of Police
Independent Pilots Association
Industrial Workers of the World
International Longshore and Warehouse Union
International Union of Journeymen and Allied Trades
International Union Security * Police * Fire Professionals of America
Jockeys' Guild
Major League Baseball Players Association
Major League Soccer Players Union
National Alliance of Postal and Federal Employees
National Education Association
National Emergency Medical Services Association
Programmers Guild
National Hockey League Players Association
National Basketball Players Association
National Rural Letter Carriers Association
National Treasury Employees Union
National Weather Service Employees Organization
Patrolmen's Benevolent Association
Philadelphia Artists Equity
Professional Hockey Players' Association
Professional Lacrosse Players' Association
Southwest Airlines' Pilots Association
Stage Directors and Choreographers Society
United Brotherhood of Carpenters and Joiners of America
United Electrical, Radio and Machine Workers of America
United Independent Technology Technicians Of America
World Umpires Association
Writers Guild of America, West
Union Reform Groups
Labor Notes
Teamsters for a Democratic Union

See also
Labor unions in the United States
List of trade unions in Canada
List of trade unions in France
List of trade unions in Germany
List of trade unions in the United Kingdom
United States labor law
Notes