Ind. Code § 6-3-4-2
(e) Where separate returns are made by husband and wife pursuant to the Internal Revenue Code, separate returns shall be made pursuant to this article.
Formerly: Acts 1963(ss), c.32, s.402; Acts 1965, c.233, s.17. As amended by Acts 1977(ss), P.L.4, SEC.9; P.L.3-1989, SEC.39.