Security Executive Agent Directive 2: Use of Polygraph in Support of Personnel Security Determinations for Initial or Continued Eligibility for Access to Classified Information or Eligibility to Hold a Sensitive Position (Effective: 14 September 2014) [open pdf - 3MB]
"This Security Executive Agent (SecEA) Directive establishes policy and assigned responsibility governing the use of polygraph examinations conducted by agencies in support of personnel security vetting for initial or continued use eligibility for access to classified information or eligibility to hold a sensitive position. Polygraph examination conducted for an reason other than those stated above, including examinations in connection with criminal law investigations and suitability determinations are not covered by this Directive."
Security Executive Agent Directive 2
U.S. Office of the Director of National Intelligence: https://www.dni.gov/