| 1 | UNI | United Air Charters | Callsign: Unitair, ICAO designator changed to UAC | ZW | AVCODES |
| 2 | UNI | Community Express Airlines Ltd. | IATA: 5V, Callsign: Community, Ceased operations. | GB | AVCODES |
| 3 | UNI | Universal Airlines | LCC of Air Europa | E | AVCODES |
| 4 | UNI | Unicair GmbH | Callsign: Unicair, | D | AVCODES |
| 5 | UNI | Unity Railways Co. | 1/1975-1/1980; eliminated 7/1986 | | NAKINA |
| 6 | UNI | Unity Railways Co. | 1/75-1/80; eliminated 7/86 | | NRHS |
| 7 | UNI | UNITY RAILWAYS | | | PWRC |
| 8 | UNI | Unity Railways | | | RSRV |
| 9 | UNI | UNIFERR Srl. | | I | TRAFFIC |
| 10 | UNIA | UNITED AMERICAN LINES | | | SCAC4 |
| 11 | UNIB | University Bus | | GB | TRAFFIC |
| 12 | UNIC | UNITED TRUCKING COMPANY | | | SCAC4 |
| 13 | UNICZ | UNILEASING a.s. | | CZ | VKM |
| 14 | UNID | UNITED MOVING AND STORAGE INC | | | SCAC4 |
| 15 | UNIDO | Unipetrol Doprava a.s. | | CZ | TRAFFIC |
| 16 | UNIDO | UNIPETROL DOPRAVA, a.s. | | CZ | VKM |
| 17 | UNIE | UNIEXPRESS TRANSPORTATION | | | SCAC4 |
| 18 | UNIF | UNIFILT CORPORATION | | | SCAC4 |
| 19 | UNIG | UNIFI INC | | | SCAC4 |
| 20 | UNIH | UNITED HAULING CORPORATION | | | SCAC4 |
| 21 | UNIK | UNITED TRANSPORT TANK CONTAINERS IN | | | SCAC4 |
| 22 | UNIM | UNIVERSAL MAIL DELIVERY SERVICE | | | SCAC1 |
| 23 | UNIM | UNIVERSAL MAIL DELIVERY SERVICE | | | SCAC4 |
| 24 | UNIN | UNIONDALE HOLDINGS | | | SCAC4 |
| 25 | UNIO | UNITED OIL HEAT INC | | | SCAC4 |
| 26 | UNIP | UNISHIPPERS | | | SCAC4 |
| 27 | UNIQ | UNIQUE TRUCKING EXPRESS INC | | | SCAC4 |
| 28 | UNIR | UNISHIPPERS | | | SCAC4 |
| 29 | UNIS | UNITED STATES ARMORED CO | | | SCAC4 |
| 30 | UNIU | UNITAS CONTAINERS LIMITED | | BM | BIC |
| 31 | UNIU | UNITAS SERVICES LTD | | | SCAC4 |
| 32 | UNIW | UNIWORLD LOGISTICS PTE LTD | | | SCAC4 |
| 33 | UNIWORLD | Uniworld Tours Inc. | | USA | TRAFFIC |
| 34 | UNIX | United Protective Car Co. | 7/1935 | | NAKINA |
| 35 | UNIX | Unigas, Inc. | added 7/1962; 7/1965-4/1970; eliminated 7/1971 | | NAKINA |
| 36 | UNIX | Unified Environmental Services Group, LLC | 7/2005 (not listed) | | NAKINA |
| 37 | UNIX | Unigas, Inc. | 7/65-4/70 | | NRHS |
| 38 | UNIX | *UNIGAS, INC. | | | PWRC |
| 39 | UNIX | +UNIFIED ENVIRONMENTAL SERVICES GROUP, LLC | | | PWRC |
| 40 | UNIX | UNIFIED ENVIRONMENTAL SERVICES GROU | | | SCAC4 |
| 41 | UNIY | UNITED DISTRIBUTION SERVICES INC | | | SCAC4 |
| 42 | UNIZ | UNITED INDUSTRIES | | | PWRC |
