Except for a contract between a public utility and a municipal corporation to furnish service at the regularly filed and published tariff rates, no contract or agreement between any public utility and any municipal corporation shall be valid unless filed with the commission at least 30 days prior to its effective date. Upon notice to the municipal authorities, and the public utility concerned, the commission may, prior to the effective date of such contract or agreement, institute proceedings to determine the reasonableness, legality or any other matter affecting the validity thereof. Upon the institution of such proceedings, such contract or agreement shall not be effective until the commission grants its approval thereof.