5 C.F.R. § 551.202 : Administrative Personnel — OFFICE OF PERSONNEL MANAGEMENT — CIVIL SERVICE REGULATIONS — PAY ADMINISTRATION UNDER THE FAIR LABOR STANDARDS ACT — EXEMPTIONS AND EXCLUSIONS — General principles

In all exemption determinations, the agency must observe the following principles:

(a) Each employee is presumed to be FLSA nonexempt unless the employing agency correctly determines that the employee clearly meets the requirements of one or more of the exemptions of this subpart and such supplemental interpretations or instructions issued by OPM. The agency must designate an employee FLSA exempt when the agency correctly determines that the employee meets the requirements of one or more of the exemptions of this subpart and such supplemental interpretations or instructions issued by OPM.
(b) Exemption criteria must be narrowly construed to apply only to those employees who are clearly within the terms and spirit of the exemption.
(c) The burden of proof rests with the agency that asserts the exemption.
(d) An employee who clearly meets the criteria for exemption must be designated FLSA exempt. If there is a reasonable doubt as to whether an employee meets the criteria for exemption, the employee will be designated FLSA nonexempt.
(e) While established position descriptions and titles may assist in making initial FLSA exemption determinations, the designation of an employee as FLSA exempt or nonexempt must ultimately rest on the duties actually performed by the employee.
(f) Although separate criteria are provided for the exemption of executive, administrative, and professional employees, those categories are not mutually exclusive. Employees who perform a combination of exempt duties set forth in this regulation may also qualify for exemption. For example, an employee whose primary duty involves a combination of exempt administrative and exempt executive work may qualify for exemption, i.e. , work that is exempt under one section of this part will not defeat the exemption under any other section.
(g) Failure to meet the criteria for exemption under what might appear to be the most obvious criteria does not preclude exemption under another category. For example, an engineering technician who fails to meet the professional exemption criteria may be performing exempt administrative work, or an administrative officer who fails to meet the administrative criteria may be performing exempt executive work.
(h) Although it is normally feasible and more convenient to identify a single exemption category, this is not always appropriate. An exemption may be based on a combination of functions, no one of which constitutes the primary duty, or the employee's primary duty may involve two categories which are intermingled and difficult to segregate. This does not preclude designating an employee FLSA exempt, provided the work as a whole clearly meets the other exemption criteria. The agency is responsible for showing and documenting that the work as a whole clearly meets one or more of the exemption criteria.

5 C.F.R. § 551.202