Massachusetts General Laws Part I. Administration of the Government (Ch. 1-182) Ch. 33, § 3

The militia shall consist of two classes, namely, the organized militia, composed and organized as provided in this chapter, and the remainder, to be known as the unorganized militia. The unorganized militia shall not be subject to duty except in case of war, actual or threatened, invasion, the prevention of invasion, threats to homeland security and the assisting of civil officers in the execution of the laws.