| Abbreviation | Definition |
|---|---|
| IPOA | Indio Police Officers Association |
| IPU | Inter Parliamentary Union |
| IPU | Inter-Parliamentary Union |
| IPU | Irish Pharmacy Union |
| IRB | International Republican Brotherhood |
| IRSA | Independent Railway Supervisors Association |
| IRU | International Romani Union |
| ISCU | Interior Savings Credit Union |
| ISCU | Ipswich and Suffolk Credit Union |
| ISSU | Independent State Store Union |
| ISSU | Indigenous Studies Student Union |
| ISSU | Indigenous Studies Students Union |
| ISU | International Stereoscopic Union |
| ISU | International Student Union |
| ISU | International Students Union |
| ISU | International Swindlers Union |
| ISUS | International Student Union Of Szeged |
| ITCU | In Touch Credit Union |
| ITGWU | Irish Transport and General Workers Union |
| ITGWU | Irish Transport General Workers Union |