No city, town, or village, whose present indebtedness exceeds the limitation imposed by this Constitution, shall be allowed to become indebted in any further amount, except as otherwise provided in this Constitution, until such indebtedness shall be reduced within such limit; provided, however, that nothing herein contained shall prevent any municipality, except the city of Gadsden, from issuing bonds already authorized by law; provided, further, that this section shall not apply to the cities of Sheffield and Tuscumbia.