5 CFR 300.301: Authority.

(a) In accordance with 5 U.S.C. 3341, an agency may detail an employee in the competitive service to a position in either the competitive or excepted service.

(b) In accordance with 5 U.S.C. 3341, an agency may detail an employee in the excepted service to a position in the excepted service and may also detail an excepted service employee serving under Schedule A, Schedule B, Schedule D, or a Veterans Recruitment Appointment to a position in the competitive service.

(c) Any other detail of an employee in the excepted service to a position in the competitive service may be made only with the prior approval of the Office of Personnel Management or under a delegated agreement between the agency and OPM.