Code of Federal Regulations Title 5. Administrative Personnel § 5.610.305 Standards

(a) Normal operations of an establishment are interrupted by events beyond the control of management or employees;

(b) For managerial reasons, the closing of an establishment or portions thereof is required for short periods;  or

(c) It is in the public interest to relieve employees from work to participate in civil activities which the Government is interested in encouraging.

(d) The circumstances are such that an administrative order under paragraph (a), (b), or (c) of this section is not appropriate and the agency under its regulations excuses, or is authorized to excuse, without charge to leave or loss of pay, employees paid on an annual basis.