| 1 | IU | Ibis Air Pty, Ltd. | | AUS | AVCODES |
| 2 | IU | Air Strabing | ICAO: MIS, | D | AVCODES |
| 3 | IU | Hevi Lift (PNG) Pty. Ltd. | Designator IU* recalled by IATA | PNG | AVCODES |
| 4 | IU | Interswede Aviation AB | Callsign: Interswede, | S | AVCODES |
| 5 | IU | Air Atlanta Icelandic | ICAO: ABD, Callsign: Atlanta, | IS | AVCODES |
| 6 | IU | SW Italia S.p.A. | ICAO: CSW, Callsign: Silkitalia, IATA Prefix: 471, AOC Revoked by ENAC on 26 September 2019. Subsidary of Silk Way West Airlines. | I | AVCODES |
| 7 | IU | PT. Super Air Jet | ICAO: SJV, Callsign: Prosper, Subsidiary of Lion Air Group. | RI | AVCODES |
| 8 | IU | Indianapolis Union | added 10/1976; 7/2000-7/2005 | | NAKINA |
| 9 | IU | (The) Indianapolis Union Ry. (Co.) | 7/1923-1/1975; eliminated 10/1976; 1/1980-1/1994; eliminated 1/1998 | | NAKINA |
| 10 | IU | Illinois Union Ry. Co. | Apr-38 | | NRHS |
| 11 | IU | Indianapolis Union Ry. | 1/52-1/94; eliminated 1/98 | | NRHS |
| 12 | IU | Indianapolis Union | Jul-00 | | NRHS |
| 13 | IU | INDIANAPOLIS UNION RAILWAY | | | PWRC |
| 14 | IU | Indianapolis Union | | | RSRV |
| 15 | IUIC | ITL USA INC | | | SCAC4 |
| 16 | IUKG | ISLANDWIDE COURIER INC | | | SCAC4 |
| 17 | IUMC | INTERUNITY MANAGEMENT CORPORATION S | | | SCAC4 |
| 18 | IUS | Icarus | Callsign: Icarus, | I | AVCODES |
| 19 | IUS | Icarus | | | ICAO1 |
| 20 | IUSI | INTERLOG USA INC | | | SCAC4 |
| 21 | IUTR | IMPERIAL TRANSPORT CO LTD | | | SCAC4 |
| 22 | IUX | Industrias Unidas de Nuevo Laredo, S.A. | 1/1943-7/1965; eliminated 10/1965 | | NAKINA |
| 23 | IUX | Industrias Unidas de Nuevo Laredo, S.A. | 1/52-7/65; eliminated 10/65 | | NRHS |
| 24 | IUX | INDUSTRIAS UNIDAS DE NUEVO LAREDO, SA | | | PWRC |
