Mass. Gen. Laws ch. 62C § 27
If, before the expiration of the time prescribed under section twenty-six for the assessment of any tax, the commissioner and the taxpayer consent in writing to extend the time for the assessment of the tax, the commissioner or his duly authorized representative may examine the books, papers, records, and other data of the taxpayer, may give any notice required by section twenty-six and may assess the tax at any time prior to the expiration of the extended time. The period so extended by the commissioner and the taxpayer may be further extended by subsequent agreements in writing made before the expiration of the time last extended. If, as a result of such examination, the commissioner determines that the taxpayer has overpaid any tax, he shall reduce the assessment accordingly and refund the overpayment in accordance with the provisions of section thirty-six.
In the case of 1 or more corporations that participated in or was required to participate in a filing through the means of a combined report under section 32B of chapter 63, the commissioner and the principal reporting corporation may consent in writing to extending the time for assessment of any component of the corporate excise reported or required to be reported under said chapter 63 by any such corporation, whether relating to the income measure, non-income measure or a minimum excise tax liability under the corporate excise. This consent shall be effective for:
Mass. Gen. Laws ch. 62C, § 27