29 CFR 779.403: Administrative and executive employees in covered enterprises employed in other than retail or service establishments.

The up-to-40 percent tolerance for nonexecutive or nonadministrative duties discussed in the preceding section, does not apply to executive or administrative employees of an establishment other than a “retail or service establishment.” For example, an executive or administrative employee of a central office or a central warehouse of a chain store system is not an employee of a “retail or service establishment,” and therefore must still devote not more than 20 percent of his hours worked in a workweek to activities which are not directly and closely related to the performance of executive or administrative duties in order to qualify as a bona fide executive or administrative employee under section 13(a)(1), except where special provisions are made in the regulations issued under that section of the Act.