No ordinance providing for the sale of any municipal utility shall be adopted except with the concurrence of three-fourths (3/4) of the members of Council and only after having been read at three (3) consecutive regular meetings. On the adoption of such an ordinance, there shall be no suspension of the rule requiring three (3) readings and the effective date of such ordinance shall be not less than ninety (90) days after the adoption thereof and the ordinance shall be subject to referendum for ninety (90) days after its passage.