Section 22L. If at any time one or more but less than all of the municipalities in which the customers of any one utility are located adopt an ordinance or by-law forbidding new installation of overhead facilities under section twenty-two C, the department of telecommunications and energy shall, in accordance with the provisions of section fourteen of chapter one hundred and fifty-nine and section ninety-four of chapter one hundred and sixty-four, after notice to all the municipalities in which such customers are located, and a hearing, establish a differential between the rates charged customers located in municipalities which have adopted such ordinance and those located in municipalities which have not adopted such ordinance, provided that no such differential, however introduced or effected, shall at any time result in revenues materially exceeding any increased cost of providing service caused solely by adoption of such ordinance by such municipality. The foregoing procedure for establishing such differential shall be exclusive.