Article XIII A Section 4 California Constitution

Below is the content of Article XIII A Section 4 of the California Constitution 

Cities, Counties and special districts, by a two-thirds vote of the qualified electors of such district, may impose special taxes on such district, except ad valorem taxes on real property or a transaction tax or sales tax on the sale of real property within such City, County or special district.

See also: Article XIII A Section 3 California Constitution