| 5260 | Antique repair and restoration (except furniture and automotives) | |
| 5240 | Antique stores, retail | |
| 5240 | Antiques, retail | |
| 2912 | Anti-scald bath and shower valves, manufacturing | |
| 2429 | Anti-scaling compounds, manufacturing | |
| 2423 | Antiseptic preparations, manufacturing | |
| 5139 | Antiseptic preparations, wholesale | |
| 2423 | Antiserums, manufacturing | |
| 1920 | Anti-skid, detachable, rubber-soled, footwear, manufacturing | |
| 2423 | Antispasmodic preparations, manufacturing | |
| 2927 | Antisubmarine projectors, manufacturing | |
| 2927 | Antitank rocket launchers, manufacturing | |
| 2423 | Antitoxins, manufacturing | |
| 2423 | Antivenoms, manufacturing | |
| 4520 | Anti-wave, anti-erosion and land reclamation works | |
| 4520 | Apartment building construction, general contractors | |
| 7010 | Apartment building operating | |
| 4520 | Apartment building, construction | |
| 7010 | Apartment buildings (five or more housing units), operators of | |
| 7010 | Apartment hotel operating | |
| 7493 | Apartment maintenance | |
| 7010 | Apartment rental or leasing | |
| 4520 | Apartments and other multiple housing, construction | |
| 1421 | Apatite mining | |
| 0122 | Apiaries | |
| 0122 | Apiculture | |
| 1429 | Aplite mining | |
| 5231 | Apothecaries, retail | |
| 3130 | Apparatus wire and cord, made in copper wire drawing plants | |
| 3130 | Apparatus wire and cord, made in non-ferrous (except aluminum, copper) wire drawing plants | |
| 3130 | Apparatus wire or cord, made in aluminum wire drawing plants | |
| 5232 | Apparel accessory stores, men's and boys', retail | |
| 5232 | Apparel accessory stores, retail | |
| 5232 | Apparel accessory stores, women's, retail | |
| 5131 | Apparel belts, men's and boys', wholesale | |
| 5131 | Apparel belts, women's and children's, wholesale | |
| 1729 | Apparel fillings (e.g., cotton mill waste, kapok), manufacturing | |
| 1729 | Apparel findings and trimmings, cut and sewn from materials owned by others | |
| 1729 | Apparel findings and trimmings, made from purchased fabric | |
| 5150 | Apparel labels (industrial supply), wholesale | |