Mass. Gen. Laws ch. 203A, § 2: Fiduciary consent

Section 2. If the individual, corporation or association maintaining a common trust fund holds property as a fiduciary together with a co-fiduciary or co-fiduciaries, investment of such property in participations in a common trust fund may be made only with the written consent of such co-fiduciary or co-fiduciaries and shall be withdrawn upon the written request of any such co-fiduciary.