Section 30B. (a) Notwithstanding any general or special law or municipal charter, vote, by-law or ordinance, 2 or more cities and towns, by vote of the city council with the approval of the mayor, in a city, and by vote of the board of selectmen, in a town, may enter into an agreement, for a term not to exceed 25 years, for joint or cooperative assessing, classification and valuation of property.

The agreement shall provide for:

(1) the division, merger or consolidation of administrative functions between or among the parties or the performances thereof by 1 city or town on behalf of all the parties;

(2) the financing of the joint or cooperative undertaking;

(3) the rights and responsibilities of the parties with respect to the direction and supervision of the work to be performed and with respect to the administration of the assessing office, including the receipt and disbursement of funds, the maintenance of accounts and records and the auditing of accounts;

(4) annual reports of the assessor to the constituent parties;

(5) the duration of the agreement and procedures for amendment, withdrawal or termination thereof; and

(6) any other necessary or appropriate matter.

(b) An agreement under this section may also provide for the formation of a single assessing department for the purpose of employing assistant assessors and necessary staff and for performing all administrative functions. An agreement may also vest in 1 person, the board of assessors of 1 of the parties or a regional board of assessors comprised of at least 1 representative from each of the parties and selected in the manner set forth in the agreement all of the powers and duties of the boards of assessors and assessing departments of the parties. In that case, the existing boards of assessors of the other parties, or of all the parties if their assessors' powers and duties are vested in 1 person, shall terminate in accordance with section 2 for the duration of the agreement. Unless the agreement provides for the board of assessors of 1 of the parties to serve as the assessors for all of the parties, or for 1 city or town to act on behalf of all parties, the agreement shall designate an appointing authority representing all of the parties. That appointing authority shall be responsible for the appointment of an assessor, assistant assessors, and other staff, and in the case of withdrawal or termination of the agreement, shall determine the employment of any employee of 1 of the parties that became part of a single assessing department. Subject to the rules and regulations established by the commissioner of revenue pursuant to section 1 of chapter 58, the agreement shall provide for qualifications, terms and conditions of employment for the assessor and employees of the assessor's office. The agreement may provide for inclusion of the assessor and the assessor's employees in insurance, retirement programs and other benefit programs of 1 of the constituent parties, but all parties to the agreement shall be pay a proportionate share of the current and future costs of benefits associated with the appointment or employment of all persons performing services for them during the duration of the agreement. A city or town party to such an agreement shall include employees under the joint assessing agreement in such programs in accordance with the terms of the agreement.

(c) A city or town may become a party to an existing agreement with the approval of the other parties.

(d) No agreement or amendment to an agreement for joint or cooperative assessing made pursuant to this section shall take effect until it has been approved in writing by the commissioner of revenue.