N.H. Rev. Stat. Ann. § 296:20

If an owner of shares, being present, either in person or by proxy, at the meeting when any assessment is voted, or being notified thereof by the treasurer or cashier by letter, shall neglect to pay the sum so assessed on his shares for 30 days after the time appointed for the payment thereof, the treasurer or cashier may sell at auction a sufficient number of his shares to pay all assessments then due from him, with necessary charges.