Mass. Gen. Laws ch. 171, § 65D
(a) Any credit union may make or acquire mortgage loans evidenced by a note which provides for variation in the rate of interest over the term of the note, but a loan made to finance or refinance the purchase of and secured by a first lien on a dwelling house of 4 or fewer separate households, occupied in whole or in part by the mortgagor, shall be subject to, but not limited to, the following conditions and restrictions imposed by the commissioner:—