A public service company shall not directly or indirectly or by any special rate, rebate, drawback, or other device or method make any deviation from the rates, fares, charges, or prices for any service rendered by it or in services rendered or to be rendered in connection therewith, as specified in its schedules of charges in effect at the time such service was rendered. No public service company may enter into any contract, agreement, or arrangement relating to the furnishing or rendering of any special product or special service not provided for or covered in the schedule without the prior approval of the Commission. However, nothing herein shall prohibit the giving by any such public service company of free or reduced rate service to its employees, or in case of public emergency, or to the classes defined and provided for in the act of Congress entitled "An act to regulate commerce" and acts amendatory thereof. Subject to the approval of the Commission, it shall be lawful for any public utility to make a contract for a definite term for its product or service. (Amended 1959, No. 329 (Adj. Sess.), § 39(b), eff. March 1, 1961; 1961, No. 263, § 5, eff. July 31, 1961.)