Mass. Gen. Laws ch. 209D, § 2-204
Simultaneous proceedings.
(a) A tribunal of the commonwealth may exercise jurisdiction to establish a support order if the petition or comparable pleading is filed after a pleading is filed in another state or a foreign country only if:
(b) A tribunal of the commonwealth may not exercise jurisdiction to establish a support order if the petition or comparable pleading is filed before a petition or comparable pleading is filed in another state or a foreign country if: