N.H. Rev. Stat. § 378:11
The provisions of RSA 378:10 shall not require absolute uniformity in the charges made and demanded by public utilities when the circumstances render any lack of uniformity reasonable, nor prevent telephone, telegraph and cable companies from entering into contracts, subject to the approval of the commission, with common carriers for the exchange of services, nor affect existing contracts relating thereto, nor prohibit a public utility from establishing differential rates or a sliding scale for the automatic adjustment of such charges if said rates or sliding scale, subject to the approval of the commission, shall be reasonable and just, nor prevent a railroad from providing tickets at reduced rates for commutation travel, excursion trips and other classes of passenger traffic subject to the approval of the commission.
RSA 378:11
1911, 164:7. PL 242 :12. RL 292:12. 1951, 203:46 par. 11, eff. Sept. 1, 1951.