Mass. Gen. Laws ch. 111 § 127N
In actions brought under this chapter against owners of residential premises a tenant may, prior to a hearing on the merits, move to join the following persons as parties: any individual, trust or corporation, partnership, association or other person who, acting alone or with another, has the authority to decide whether to rehabilitate, or sell or otherwise dispose of the premises, with or without record title or recorded interest. Such person shall not be joined, however, if its decision-making authority is derived solely from its position as a fiduciary if such person has never personally had any financial or possessory interest in the premises.
If the court finds that the owner may be unable for financial reasons or otherwise to perform any act or pay any liability that may be ordered if judgment is entered for the tenant, the court shall allow the motion joining any such person. The owner and any person so joined shall be jointly and severally liable for taking any action or paying any damages ordered by the court; provided, however, that the provisions of this section regarding the liability of persons other than owners shall not apply to two and three family owner-occupied residential premises.
Mass. Gen. Laws ch. 111, § 127N