4 C.F.R. § 25.3
A person may be admitted to the GAO Building after presentation of personal identification to conduct lawful business with GAO, its employees, or other tenants of the GAO Building and for any other purposes authorized by the Comptroller General or his designee. During normal working hours, the GAO Building shall be open to the public unless specific circumstances require it to be closed to the public to ensure the orderly conduct of government business. Outside of normal working hours, the GAO Building shall be closed to the public unless the Comptroller General or his designee has approved the after-normal-working-hours use of the Building or portions thereof. When the Building, or a portion thereof, is closed to the public, admission will be restricted to authorized persons who shall register upon entry and exit, and shall, when requested, display government or other identifying credentials to the guards, security staff, or other authorized individuals. Failure to comply with such a request is a violation of these regulations.
4 C.F.R. § 25.3