N.H. Rev. Stat. Ann. § 266-A:17

No common carrier by motor vehicle shall charge or demand or collect or receive a greater or lesser or different compensation for transportation or for any service in connection therewith between the points enumerated in such tariff than the rates, fares, and charges specified in the tariffs in effect at the time; and no such carrier shall refund or remit in any manner or by any device, directly or indirectly, or through any agent or otherwise, any portion of the rates, fares, or charges so specified, or extend to any person any privileges or facilities for transportation between points in this state except such as are specified in its tariffs.