In case a petition be filed requiring that an ordinance passed by the commission involving the expenditure of money, a bond issue or a public improvement be submitted to a vote of the voters, all steps preliminary to such actual expenditure, actual issuance of bonds, or actual execution of the contract for such improvement, may be taken prior to the election; provided, that the provisions of this article shall not apply to any ordinance which comes within the provisions of the bond and warrant laws of the State of Texas, nor shall the same apply to any ordinance authorizing the issuance of tax or revenue bonds which have been previously authorized by a vote of the people.