To accurately determine the correct amount of Massachusetts withholding, employers will rely on Massachusetts Form M4. Step 1 – Register as an Employer.Step 2 – Employee Eligibility Verification. For complete instructions on how to complete this form, please watch our "How to Fill Out the Commonwealth Agency New Member Enrollment Form" video. Payroll tax registration is required for all employers in Massachusetts to ensure compliance with state tax laws and to properly withhold and remit taxes. Please note that you may fill out the following form electronically or on paper. Fill out your form and print it. Use our Form Filler tool to fill out your form on a desktop or laptop computer and then print it. The table lists the various MA forms and envelopes available to providers. Use this tool to get an EIN directly from the IRS in minutes for free.