SECTION 1. Chapter 59 of the General Laws is hereby amended by striking out section 5I and inserting in place thereof the following section:—

Section 5I. With respect to each parcel of real property classified as class three, commercial, in each city or town certified by the commissioner to be assessing all property at its full and fair cash valuation, and at the option of the selectmen or mayor, with the approval of the town meeting or city council, as the case may be, there shall be an exemption equal to not more than fifty percent of the value of the parcel; provided, however, that such exemption shall only apply to property that is solely occupied by a business that, at that location and all others combined, had an assessed valuation of less than one million dollars. This exemption shall be in addition to any exemptions allowable under section five. The value of exemptions granted under this section shall be borne by the combined value of class three commercial property and class four industrial property.