| Abbreviation | Definition |
|---|---|
| CSFU | Calasiao Sales Force Union |
| CSKU | Civic Safai Karamchari Union |
| CSSU | Chittenden South Supervisory Union |
| CSSU | Computer Science Student Union |
| CSTA | Computer Science Teachers Association |
| CSTU | Civil Servants Trade Union |
| CSTU | Civil Service Trade Union |
| CSU | Christian Social Union |
| CSU | Christlich Soziale Union |
| CSUE | Carver Scott United Educators |
| CTAU | Catholic Total Abstinence Union |
| CTF | Canadian Teachers' Federation |
| CTFU | Cyprus Turkish Farmers Union |
| CTU | Caribbean Telecommunications Union |
| CTU | Catholic Theological Union |
| CTU | Chicago Teachers Union |
| CTU | Clerical Technical Union |
| CTUA | Confederation of Trade Unions of Armenia |
| CTUF | Campaign for Trade Union freedom |
| CTUF | Ceylon Trade Union Federation |