The governing body of any county, city or town is hereby authorized to impose and collect a service charge on the owners of all real estate within its jurisdiction which is exempted from local real estate taxation by international law or by any treaty, international agreement or statute under the United States Constitution. Such service charge shall be calculated as provided in § 58.1-3400, and shall be based on the assessed value of the real estate and the amount which the county, city or town expends for those services for which the applicable law, treaty, agreement or statute permits a charge to be imposed. The service charge shall be based on the amount expended in the fiscal year preceding the year such charge is assessed. The governing body may impose a service charge of a lower amount than authorized or no service charge, as it may determine in the exercise of its legislative power.