Iowa Code § 373.10: Taxing authority.

The metropolitan council shall have the authority to levy city taxes to the extent the city tax levy authority is transferred by the charter to the metropolitan council. A member city shall transfer a portion of the city’s tax levy authorized under section 384.1 or 384.12, whichever is applicable, to the metropolitan council. The maximum rates of taxes authorized to be levied under sections 384.1 and 384.12 by a member city shall be reduced by an amount equal to the rates of the same or similar taxes levied in the city by the metropolitan council.