The board of county commissioners of any of the several counties, or any representative thereof in its place or stead, or any city council or board of city commissioners or any representative thereof, any township supervisors, or representative groups of taxpayers or taxpayers' associations, or any individual representing the same, may appear before the state board of equalization to be heard for the purpose of opposing any unreasonable or unjust increase or decrease in the valuation of the taxable property of the county, city, or township represented as equalized by the county board of equalization, or of opposing any increase or decrease in such valuation as proposed by the state board of equalization, to the end that all valuations of like taxable property may be uniform and equal throughout the state.