N.H. Rev. Stat. Ann. § 47:26

No such ordinance or amendments or supplements thereto, as hereinbefore set forth, shall become effective or be altered until after a public hearing in relation thereto, at which parties in interest and citizens shall have an opportunity to be heard. Notice of the time and place of such hearing shall be published in a paper of general circulation in the state at least 15 days before the holding of said hearing.