N.H. Rev. Stat. Ann. § 38-A:17

The authority may fix rates, fares, tolls, charges, rents or other charges for the use of the system acquired, constructed, operated, or maintained by the authority and may alter, change, or modify the same, all subject to the covenants of any revenue bond indenture pursuant to which revenue bonds have been issued and are outstanding which contains covenants entered into by the authority with respect to the fixing of such rates, fares, tolls, charges, and rents.