29 CFR §779.308

In order to meet the requirement of actual employment “by” the establishment, an employee, whether performing his duties inside or outside the establishment, must be employed by his employer in the work of the exempt establishment itself in activities within the scope of its exempt business. (See Davis v. Goodman Lumber Co., 133 F. 2d 52 (CA-4) (holding section 13(a)(2) exemption inapplicable to employees working in manufacturing phase of employer's retail establishment); Wessling v. Carroll Gas Co., 266 F. Supp. 795 (N.D. Iowa); Oliveira v. Basteiro, 18 WH Cases 668 (S.D. Texas). See also, Northwest Airlines v. Jackson, 185 F. 2d 74 (CA-8); Walling v. Connecticut Co., 154 F. 2d 522 (CA-2) certiorari denied, 329 U.S. 667; and Wabash Radio Corp. v. Walling, 162 F. 2d 391 (CA-6).)