Often the local Merit Promotion Plan or Labor Agreements will dictate how the interview panel process will be conducted.
In all cases, when an interview panel is used, the interview panel will only be comprised of Federal employees.
DoDI 1100.21 and AR 608-1, provide that "Volunteers may not hold policy making positions, supervise paid employees or military personnel, or perform inherently governmental functions."
OMB Policy Letter 92-1 defines "inherently governmental functions" as functions that are so intimately related to the public interest as to mandate performance by government employees.
Subpart 7.5 of the Federal Acquisition Regulation provides a list of functions considered as inherently governmental functions or which shall be treated as such; specifically, "The selection or non-selection of individuals for Federal Government employment, including the interviewing of individuals for employment".