From the Hotline: Purpose of Massachusetts M-4 Form

Question:Can you please confirm what the Massachusetts M-4 Form is and what it is used for?

Answer: The Massachusetts M-4 Employee Withholding Tax Form is used to determine an employee’s withholding amount for state tax purposes only. If an employee chooses to use the same withholdings for federal and state taxation, they may complete the federal W-4 which may then be used for both purposes. If an employee would like a different amount withheld for state taxes than what is held for federal, whether it is a number of exemptions and/or a flat dollar amount, they will need to complete an M-4.

Source: http://www.mass.gov/dor/docs/dor/forms/wage-rpt/pdfs/m-4.pdf