| Abbreviation | Definition |
|---|---|
| CMCU | Central Murray Credit Union |
| CMCU | Charlotte Metro Credit Union |
| CMIU | Cigar Makers International Union |
| CMLU | Ceylon Moor Ladies Union |
| CMTU | Confederation of Malta Trade Unions |
| CMTU | Confederation of Mongolian Trade Unions |
| CNETU | Congress of Non European Trade Unions |
| CNETU | Council of Non European trade unions |
| CNSU | Caledonia North Supervisory Union |
| COBT | Central Ontario Building Trades |
| COBUS | College of the Bahamas Union of Students |
| COCU | Consultation On Church Union |
| COEASU | College Of Education Academic Staff Union |
| COGUA | Church Of God of the Union Assembly |
| COIU | China Overseas Investment Union |
| COIU | Congress of Independent Unions |
| COMBO | Collective Of Musicians of Belfast Organisation |
| CONGU | Council of National Golf Unions |
| CONSAWU | Confederation of South African Workers' Unions |
| COSATU | Congress Of South Africa Trade Unions |