In a 2003 decision, the Massachusetts Appellate Court expanded this prohibition on removal to include relocation within the Commonwealth if the relocation would "involve significant disruption of the noncustodial parent's visitation rights and the parents cannot agree." D.C. v. J.S., 58 Mass. App. Ct. 351, 355-356 (2003).
If your ex is threatening to move to another part of the state with your children and it would significantly disrupt your parenting time with the children, then you can ask the Court to prevent this move. If the Court agrees that the move would significantly disrupt your parenting time then the court should apply the same standard as in a case involving a removal out of state. It may be prudent for a parent who wants to move, even within the Commonwealth, to ask the Court's permission if the other parent disagrees. This could prevent costly requirements if the Court disallowed the move afterwards.