Massachusetts General Laws Part I. Administration of the Government (Ch. 1-182) Ch. 154, § 4

No assignment under section three shall be valid unless a copy thereof is delivered to the assignor by the assignee at the date of the execution of such assignment.  No such assignment shall be binding on the employer of the assignor until a copy of the assignment and a written account, which shall conform to the requirements hereinafter stated, have been delivered to said employer.  The account shall contain a statement of the balance due and of the sums of money received by the assignee, together with the date of every such payment and a statement as to whether such payment is interest, a payment on the principal, or, in case of a loan, a payment on the charge for making and securing it.