29 CFR §510.22

1. (a)Appendix A contains a listing of all industries included in the Census of Manufacturing. Appendix B contains a listing of non-manufacturing industries. These listing are organized by SIC numbers, presented by:
   1. (1)Major group (two-digit classification),
   2. (2)Industry group (three-digit classification), and (3) industry (four-digit classification). In each instance the phase-in tier which applies to that industry or group is indicated.
2. (b)Employers are required to utilize the most detailed classification which applies to their industry. Where an employer's four-digit SIC code is listed, the tier applicable to that code determines the minimum wage phase-in schedule for that employer. (See § 510.10, above).
3. (c)Where an industry is not listed by four-digit SIC code, employers shall utilize the three-digit which applies to their industry. If a three-digit code is not listed, employers shall use the applicable two-digit code.