| Abbreviation | Definition |
|---|---|
| CHW | Community Health Workers |
| CIAU | Canadian Interuniversity Athletics Union |
| CICU | Central Illinois Credit Union |
| CIO | Congress of Industrial Organizations |
| CIRB | Canada Industrial Relations Board |
| CISL | Confédération Internationale des Syndicats Libres (French: International Confederation of Free Trade |
| CISNU | Confederation of Iranian Students, National Union |
| CITA | Canberra Indonesian Teachers Association |
| CITU | Centre for Indian Trade Unions |
| CITU | Centre of Indian Trade Unions |
| CIU | Confederation of Independent Unions in the Public Sector |
| CIU | Confederazione Italiana Unionquadri |
| CIWU | Commercial and Industrial Workers Union |
| CLA | Collective Labor Agreement |
| CLA | Council of Labor Affairs |
| CLC | Canadian Labour Congress |
| CLOUD | Communities and Libraries Online Union Database |
| CLUW | Coalition of Labor Union Women |
| CMAW | Construction Maintenance and Allied Workers |
| CMCU | Central Minnesota Credit Union |