N.H. Rev. Stat. Ann. § 356-C:10

If a tenant refuses to pay a permissible rent increase under RSA 356-C:6, I(a), or brings an action under RSA 356-C:9, I, on grounds found by a court in either case to be frivolous or solely for the purposes of harassment, the tenant shall be liable to the owner for any costs incurred by the owner in connection with any such proceedings, including reasonable attorney's fees.