An employee shall not participate, while on Government-owned or leased property or while on duty for the Government, in any gambling activity including the operation of a gambling device, in conducting a lottery or pool, in a game for money or property, or in selling or purchasing a numbers slip or ticket. However, this section does not preclude activities:

(a) Necessitated by an employee's law enforcement duties; or

(b) Under section 3 of Executive Order 10927 and similar agency-approved activities.