All persons employed or assigned to duties under this chapter shall be investigated to insure that the employment or assignment is consistent with the national interest in accordance with standards and procedures established by the President. If an investigation made pursuant to this section develops any data reflecting that the person who is the subject of the investigation is of questionable loyalty or is a questionable security risk, the investigating agency shall refer the matter to the Federal Bureau of Investigation for the conduct of a full field investigation. The results of that full field investigation shall be furnished to the initial investigating agency, and to the agency by which the subject person is employed, for information and appropriate action. Volunteers shall be deemed employees of the United States Government for the purpose of this section.