(1) If the federal income tax liabilities of both spouses are determined on a joint federal return for the taxable year, they must file a joint return under this chapter.
(2) Except as otherwise provided in this subsection, if the federal income tax liability of either spouse is determined on a separate federal return for the taxable year, they must file separate returns under this chapter. State registered domestic partners may file a joint return under this chapter even if they filed separate federal returns for the taxable year.
(3) The liability for tax due under this chapter of each spouse or state registered domestic partner is joint and several, unless:
(a) The spouse is relieved of liability for federal tax purposes as provided under Title 26 U.S.C. Sec. 6015 of the internal revenue code; or
(b) The department determines that the domestic partner qualifies for relief as provided by rule of the department. Such rule, to the extent possible without being inconsistent with this chapter, must follow Title 26 U.S.C. Sec. 6015.