Mass. Gen. Laws ch. 171 § 39
Shares and deposits may be received and held in the name of a member with one or more persons as joint tenants, payable to such member or his survivors, and any part or all of the shares or deposits and dividends or interest represented by joint accounts may be withdrawn, assigned or transferred by any of the individual parties. Payment to any of the parties to a joint account while all of them are living shall discharge the liability of the corporation to all parties and in the event of the death of any of them the corporation shall be liable only to the survivors, and the payment to any of the survivors shall discharge the liability of the corporation to all parties.
No person holding an account as a joint tenant with a member as provided herein and who is not a member or is not otherwise eligible for membership shall be deemed a member for any other provision of this chapter.
The surviving owner or owners of a joint account may maintain the balance of the account in the amount appearing at the time of the decease of a joint owner, and such credit union may allow dividend or interest additions and accumulations thereon. Such shares or deposits or any part thereof, or any interest dividends thereon, may be paid to any such person or to any assignee or pledgee of any of such persons whether the other such persons be living or not, provided they are not then attached at law or in equity in a suit against any such person and the credit union then has no notice in writing of any assignment or pledge of the account by any of such persons to any person other than the person to whom payment is being made hereunder. All such payments shall be valid. A surviving owner of a joint account may continue credit union membership if the surviving owner is eligible for membership and meets all requirements in the by-laws
Mass. Gen. Laws ch. 171, § 39