N.H. Rev. Stat. Ann. § 5:18-a

In addition to any other requirements, no contract for personal services, under which the total of payments equals $2,500 or more, in lump sum or installments, between the state and a nonresident corporation, partnership or association or between the state and a resident doing business under a name other than his own, shall be valid unless the contract shall have attached to it evidence of registration with the secretary of state as required under RSA 293-A, 305-A or 349. This requirement shall not apply to a nonresident corporation not organized for profit, except that each contract between the state and a resident or nonresident corporation, partnership or association shall have attached to the contract evidence of authority of the parties to execute and be bound by the contract.