29 CFR 779.112: Office employees.

Similarly office employees of retail businesses who regularly and recurrently check records of and make payments for goods shipped to their employer from outside of the State, or regularly and recurrently keep records of or otherwise work on the accounts of their employer's out-of-State customers, or who regularly and recurrently prepare or mail letters, checks, reports or other documents to out-of-State points, are engaged both in commerce and in the production of goods for commerce within the meaning of the Act. Likewise, timekeepers who regularly and recurrently prepare and maintain payrolls for and pay employees who are engaged in commerce or in the production of goods for commerce are themselves engaged in covered activities.