The voters shall have power to propose any ordinance except an ordinance appropriating money or authorizing the levy of taxes, and to adopt or reject the same at the polls, such power being known as the initiative. Any initiative ordinance may be submitted to the Council by a petition signed by currently qualified voters of the city equal in number to at least ten (10) percent of the total number of the qualified voters registered to vote at the last regular municipal election. To be valid, a petition be submitted for the purpose of complying with an initiative election process shall comply with the Texas Election Code, as amended and shall be for a subject for which the initiative election process is authorized by state law.