From and after the passage of this act all municipalities or corporations, employing policemen within the commonwealth of Pennsylvania, shall pay to all such policemen a fixed or stipulated salary; and that hereafter it shall not be lawful for any such policeman to charge or accept any fee or other compensation, in addition to his salary, for any service rendered or performed by him of any kind or nature whatsoever pertaining to his office or duties as a policeman, except public rewards and the legal mileage allowed for traveling expenses.
53 P.S. § 633