18-125-810 Me. Code R. § .02
A taxable corporation that is a member of an affiliated group and that is engaged in a unitary business with one or more other members of that affiliated group must file a combined report. 36 M.R.S. §5220(5). Maine utilizes a "water's edge" methodology for determining the apportionable income base, meaning the income subject to apportionment is the income required to be reported on the taxpayer's federal income tax return as modified by Maine law. Therefore, all unitary members of the affiliated group, except those members not required to file a federal return, must be listed on the combined report. Furthermore, the income of a corporation not required to file a federal return may not be included on the combined report. The apportionment factor must include only those amounts attributable to the apportionable income base for that taxable year. Variation may be allowed when petitioned for by the taxpayer or may be required by the Assessor. See 36 M.R.S. §5211(17).
The combined report must indicate whether each corporation has nexus with Maine. The combined report must also include, both in the aggregate and by corporation: the federal taxable income, state modifications provided by 36 M.R.S. §5200- A, sales in Maine and everywhere, and the Maine net income of the unitary business. See 36 M.R.S. §5244. The corporations listed that are unitary members of the affiliated group and that have nexus with Maine must file a Maine corporate income tax return or returns as provided in section .05 below. See 36 M.R.S. §5220(5).
18-125 C.M.R. ch. 810, § .02