| 3691 | Clay tile manufacturing | |
| 3691 | Clay wall tile manufacturing | |
| 3824 | Clay working and tempering machine manufacturing | |
| 3824 | Cleaner, boiler tube, manufacturing | |
| 3829 | Cleaning and pressing equipment manufacturing | |
| 3523 | Cleaning compound manufacturing | |
| 5000 | Cleaning oil wells, contract services | |
| 3523 | Cleaning powder manufacturing | |
| 3523 | Cleaning preparation manufacturing | |
| 1120 | Cleaning service, grain | |
| 9520 | Cleaning, dyeing and pressing service | |
| 9200 | Cleaning, window | |
| 3523 | Cleanser, containing soap, manufacturing | |
| 3523 | Cleanser, soapless, manufacturing | |
| 3419 | Cleansing tissue paper manufacturing from stock | |
| 8103 | Clearing house association | |
| 1120 | Clearing services, agricultural land, not involving construction | |
| 3811 | Cleaver manufacturing | |
| 3220 | Clerical clothing cutting and sewing | |
| 9331 | Clinic | |
| 3819 | Clip, paper, base metal, manufacturing | |
| 3833 | Clipper, electric, manufacturing | |
| 3811 | Clipper, hand, manufacturing | |
| 9332 | Clipping animal, pet | |
| 3220 | Cloak cutting and sewing | |
| 3560 | Clock and watch part, plastic, manufacturing | |
| 3853 | Clock manufacturing | |
| 3853 | Clock movement manufacturing | |
| 9514 | Clock repairing | |
| 3853 | Clock, electric, manufacturing | |
| 3853 | Clock, electronic, manufacturing | |
| 9511 | Clog repairing | |
| 3319 | Clog sole manufacturing | |
| 3319 | Clog, wooden, manufacturing | |
| 3610 | Closet bowl manufacturing | |
| 3220 | Cloth cap manufacturing | |
| 3823 | Cloth cutting die manufacturing | |
| 9520 | Cloth reweaving and mending | |
| 3824 | Cloth spreading machine manufacturing | |
| 3212 | Cloth, polishing, chemically treated, cutting and sewing | |