| 1401 | UPAX | Utah Poultry Producers Cooperative Association Refrigerator Line (North American Car Corp.) | 7/1935 | | NAKINA |
| 1402 | UPAX | United Power Association | added 4/1982; 1/1994; eliminated 4/2000 | | NAKINA |
| 1403 | UPAX | Great River Energy | added 4/2000; 7/2000-7/2005; eliminated 10/2005 | | NAKINA |
| 1404 | UPAX | United Power Association | added 4/82; 1/94; eliminated 4/2000 | | NRHS |
| 1405 | UPAX | Great River Energy | added 4/2000; 7/2000 | | NRHS |
| 1406 | UPAX | *UTAH POULTRY PRODUCERS COOPERATIVE ASSOCIATION REFRIGERATOR LINE | | | PWRC |
| 1407 | UPAX | *GREAT RIVER ENERGY [UNITED POWER ASSOCIATION] | | | PWRC |
| 1408 | UPAX | United Power Association | | | RSRV |
| 1409 | UPB | Air Foyle Charters Ltd. | Callsign: Kris, | GB | AVCODES |
| 1410 | UPB | Union Pacific Railroad | | | RSRV |
| 1411 | UPBZ | UNION PACIFIC RAILROAD COMPANY | | | PWRC |
| 1412 | UPBZ | Union Pacific Railroad | | | RSRV |
| 1413 | UPBZ | UNION PACIFIC RAILROAD | | | SCAC4 |
| 1414 | UPC | Air Foyle Airways Ltd. | Callsign: Cutlass, | GB | AVCODES |
| 1415 | UPCF | UNIQUE FREIGHT TRANSPORT INC | | | SCAC4 |
| 1416 | UPCH | UPCHURCH, DEWEY TRUCKING | | | SCAC4 |
| 1417 | UPCR | UNITED PETROLEUM CARRIERS | | | SCAC4 |
| 1418 | UPCS | UNION PACIFIC CARRIER SERVICES | | | SCAC4 |
| 1419 | UPCU | (UPCX) USPCI, INC. | | | PWRC |
| 1420 | UPCU | USPCI Inc. | | | RSRV |
| 1421 | UPCU | USPCCI | | | SCAC4 |
| 1422 | UPCX | Universal Portland Cement Co. | 7/1923 | | NAKINA |
| 1423 | UPCX | Universal Portland Cement Co. (Universal Atlas Cement Co.) | 7/1930-7/1935 | | NAKINA |
| 1424 | UPCX | Universal Atlas Cement Co. | 7/1937-4/1938 | | NAKINA |
| 1425 | UPCX | Union Petroleum Corp. | added 1/1962; 7/1965-4/1970; eliminated 4/1974 | | NAKINA |
| 1426 | UPCX | Home Petroleum Corp. | added 4/1974; 1/1975; eliminated 10/1979; 1/1980 | | NAKINA |
| 1427 | UPCX | USPCI c/o Laidlaw Environmental Services, Inc. | added 10/1995; eliminated 4/1996 | | NAKINA |
| 1428 | UPCX | Laidlaw Environmental Services, Inc. | added 4/1996; 7/2000; eliminated 4/2002 | | NAKINA |
| 1429 | UPCX | Clean Harbors Environmental Sciences, Inc. | 7/2005 (not listed) | | NAKINA |
| 1430 | UPCX | Universal Portland Cement Co. (Universal Atlas Cement Co.) | Apr-38 | | NRHS |
| 1431 | UPCX | Union Petroleum Corp. | added 1/62; 7/65-4/70 | | NRHS |
| 1432 | UPCX | Home Petroleum Corp. | 1/75-1/80 | | NRHS |
| 1433 | UPCX | USPCI c/o Laidlaw Environmental Services, Inc. | added 10/95; eliminated 4/96 | | NRHS |
| 1434 | UPCX | Laidlaw Environmental Services, Inc. | added 4/96; 7/2000 | | NRHS |
| 1435 | UPCX | *UNIVERSAL ATLAS CEMENT CO. [UNIVERSAL PORTLAND CEMENT CO.] | | | PWRC |
| 1436 | UPCX | *HOME PETROLEUM CORP. [UNION PETROLEUM CORP.] | | | PWRC |
| 1437 | UPCX | +CLEAN HARBORS ENVIRONMENTAL SCIENCES, INC [LAIDLAW ENVIRONMENTAL SERVICES INC.; USPCI, INC.] | | | PWRC |
| 1438 | UPCX | Laidlaw Environmental Services | | | RSRV |
| 1439 | UPCX | CLEAN HARBORS ENVIRONMENTAL SERVICE | | | SCAC4 |
| 1440 | UPD | Air Foyle Charter Airlines Ltd. | IATA: G2, Callsign: Broadsword, Name changed to Air Foyle Passenger Airlines Limited | GB | AVCODES |
| 1441 | UPD | Air Foyle Passenger Airlines Limited | IATA: G2, Callsign: Broadsword, Designator G2 recalled by IATA. Name changed from Air Foyle Charter Airlines Ltd. | GB | AVCODES |
| 1442 | UPDC | UNION PACIFIC CARRIER SERVICES (DIV | | | SCAC4 |
| 1443 | UPDL | U-PAK DISPOSALS (1989) LIMITED | | | SCAC4 |
| 1444 | UPDM | UNION PACIFIC DE MEXICO | | | SCAC1 |
| 1445 | UPDT | UPPER DECK TRANSPORT INC | | | SCAC4 |
| 1446 | UPET | UNIFIED PETROLEUM | | | SCAC4 |
| 1447 | UPFE | Union Pacific R.R. Co. | 1/1975-7/2005 | | NAKINA |
| 1448 | UPFE | Union Pacific R.R. Co. | 1/75-7/2000 | | NRHS |
| 1449 | UPFE | UNION PACIFIC RAILROAD COMPANY [PACIFIC FRUIT EXPRESS] | | | PWRC |
| 1450 | UPFE | Pacific Fruit Express (Union Pacific Railroad) | | | RSRV |
| 1451 | UPFS | UNION PACIFIC FREIGHT SERVICE | | | SCAC1 |
| 1452 | UPFS | UNION PACIFIC DISTRIBUTION SERVICES | | | SCAC4 |
| 1453 | UPFU | (UPUU) UNION PACIFIC BULKTAINER SERVICE | | | PWRC |
| 1454 | UPFU | Union Pacific Bulktainer Service | | | RSRV |
| 1455 | UPFU | UNION PACIFIC MOTOR FREIGHT CO. | | | SCAC4 |
| 1456 | UPFX | United States Pipe and Foundry Co. | 7/1935-1/1943 | | NAKINA |
| 1457 | UPFX | United States Pipe and Foundry Co. | Apr-38 | | NRHS |
| 1458 | UPFX | UNITED STATES PIPE & FOUNDRY CO. | | | PWRC |
| 1459 | UPGA | UPS FREIGHT (GROUND) | | | SCAC4 |
| 1460 | UPGF | UPS FREIGHT | | | SCAC4 |
| 1461 | UPGS | UNITED BEST TRANSPORT CORP | | | SCAC4 |
| 1462 | UPGZ | UPS FREIGHT | | | SCAC4 |
| 1463 | UPHY | UPLANDS PHEASANTRY | | | SCAC4 |
| 1464 | UPHZ | Union Pacific Railroad | | | RSRV |
| 1465 | UPHZ | UNION PACIFIC RAILROAD COMPANY | | | SCAC4 |
| 1466 | UPIA | UNITED PRODUCTS INTERNATIONAL INC | | | SCAC4 |
| 1467 | UPIX | USS-POSCO INDUSTRIES | | | PWRC |
| 1468 | UPL | Ukrainian Pilot School | Callsign: Pilot School, | UA | AVCODES |
| 1469 | UPL | Ukrainian Pilot School | | | ICAO1 |
| 1470 | UPLD | UNITED PERISHABLE LOGISTICS LLC | | | SCAC4 |
| 1471 | UPLG | U P LOGISTICS | | | SCAC4 |
| 1472 | UPLH | UNION POWER LOGISTIC LLC | | | SCAC4 |
| 1473 | UPLL | UPLAND LOGISTIC INC | | | SCAC4 |
| 1474 | UPLT | UPLAND TRANSPORTATION INC | | | SCAC4 |
| 1475 | UPLU | UPLINE CZ, S.R.O. | | CZ | BIC |
| 1476 | UPM | Union Pacific R.R. Co. | 1/1980 | | NAKINA |
| 1477 | UPM | Union Pacific R.R. Co. | Jan-80 | | NRHS |
| 1478 | UPM | UNION PACIFIC RAILROAD, MILWAUKEE ROAD OPERATIONS | | | PWRC |
| 1479 | UPM | Union Pacific Railroad | | | RSRV |
| 1480 | UPMF | ULTRA-POLY MANUFACTURING INC | | | SCAC4 |
| 1481 | UPMS | UNITED PETROLEUM SERVICES INC | | | SCAC4 |
| 1482 | UPMT | UNITED PRECIOUS METAL REFINING INC | | | SCAC4 |
| 1483 | UPNC | UP NORTH CORP | | | SCAC4 |
| 1484 | UPND | UNITED PARCEL SERVICE NEXT DAY SERV | | | SCAC4 |
| 1485 | UPNZ | UNION PACIFIC RAILROAD COMPANY | | | PWRC |
| 1486 | UPNZ | Union Pacific Railroad | | | RSRV |
| 1487 | UPNZ | UNION PACIFIC RAILROAD COMPANY | | | SCAC4 |
| 1488 | UPOF | UPS OCEAN FREIGHT SERVICES INC | | | SCAC4 |
| 1489 | UPOL | UPSTATE PAVING ONE (1) LLC | | | SCAC4 |
| 1490 | UPOZ | UNITED PARCEL SERVICE | | | PWRC |
| 1491 | UPOZ | United Parcel Service | | | RSRV |
| 1492 | UPOZ | UNITED PARCEL SERVICE | | | SCAC4 |
| 1493 | UPP | Union Pacific R.R. Co. (passenger cars) | 1/1994-7/2005 | | NAKINA |
| 1494 | UPP | Union Pacific R.R. Co. (passenger cars) | 1/94-7/2000 | | NRHS |
| 1495 | UPP | UNION PACIFIC RAILROAD (PASSENGER CARS) | | | PWRC |
| 1496 | UPP | Union Pacific Railroad | | | RSRV |
| 1497 | UPPE | UPPER CANADA FOREST PRODUCTS LTD | | | SCAC4 |
| 1498 | UPPN | U. P. SPECIAL DELIVERY, INC | | | SCAC1 |
| 1499 | UPPN | U S SPECIAL DELIVERY INC | | | SCAC4 |
| 1500 | UPPS | Uppsala Bus AB | | S | TRAFFIC |
