N.H. Rev. Stat. Ann. § 666:4

The state committee of a political party may appoint a person to act as challenger of voters at any polling place in the state at a state election. A city or town committee of such a party may appoint a person to act as such challenger at any polling place in such city or town at a town election, business meeting, or city election. A statement signed by the chairman of the committee appointing him shall be sufficient evidence of the authority of any such challenger. He may be reasonably compensated for his services by the political party whose committee appointed him. He shall be assigned by the moderator or other election officer presiding at the polling place to such position within the polling place as will enable him to see and hear each voter as he offers to vote. Nothing herein contained shall deprive any other person of the right to challenge a voter as provided by law.