Mass. Gen. Laws ch. 171 § 51
No credit union shall be required to recognize an adverse claim to shares or a deposit standing on its books to the credit of or for the account of any person, except by virtue of the service upon it of appropriate process issued by a court of competent jurisdiction in a suit or action to which such person, or his executors or administrators, has been made a party, unless the adverse claimant gives bond satisfactory to the credit union and the adverse claimant to hold harmless and indemnify it from any liability, loss, damage, costs and expenses whatsoever on account of such adverse claim, or files with the credit union an affidavit setting forth facts showing a reasonable cause for belief that a fiduciary relationship exists between such person and said adverse claimant and that such person is about to misappropriate the deposit or shares in question.
Mass. Gen. Laws ch. 171, § 51