John Callahan has earned endorsements from:

Labor Organizations:

• AFL-CIO
• American Federation of Government Employees (AFGE)
• American Federation of State County and Municipal Employees (AFSCME)
• American Federation of Teachers
• American Postal Workers Union (APWU)
• Boilermakers Local #13
• Bricklayers, Tilesetters & Cement Masons Local 592 (BTCM) 
• Building and Construction Trades Department (BCTD)
• Carpenters
• Cement Masons & Plasters Local #592
• Communication Workers of America (CWA)
• Elevator Constructors Local #84
• Glaziers, Architectual Metal & Glass Workers Local #252 DC 21
• Heavy & Highway Laborers Local #158
• Insulators & Allied Workers Local #23 (Asbestos Workers)
• International Brotherhood of Electrical Workers
• Ironworkers Local #36
• Laborers Local #1174
• Machinists (IAM)
• Millwrights Local #1906
• Painters Local #1269
• Plumbers Local #690
• Road Sprinkler Fitters Local #669
• Roofers & Waterproofers Local #30
• Seafarers
• Sheetmetal Workers Local #19
• Steamfitters Local #420
• Service Employees International Union (SEIU)
• Teamsters Local 773
• United Auto Workers
• United Food and Commercial Workers
• United Steelworkers

This list is growing, so stay tuned for more endorsements.