Gujarat Provincial Municipal Corporations Act, 1949
Whenever the Corporation determines under section 104 to have recourse to supplementary taxation in any official year, it shall do so by increasing, for the unexpired portion of the said year, the rates at which any tax imposable under this Act is being levied, subject to the limit and conditions for such tax prescribed in this Act or in the orders of sanction of the '[State] Government or by levying, with due sanction, a tax imposable under this Act but not being levied at time being.