Did anyone notice that Colorado’s new civil union law purports to create a status that is the legal equivalent of marriage–except that parties to a civil union are prohibited from filing a joint state income tax return? (See § 14-15-117.) The purported reason for this is that couples who are not “married” for federal tax purposes cannot file a joint federal income tax return and the Colorado state income tax piggybacks on the federal income tax. But other states that have civil unions or same-sex marriage don’t seem to have a problem with requiring joint filing by same-sex couples (however much in the way of extra administrative burdens and extra costs it might add). (See Carlton Smith & Edward Stein, Dealing with DOMA: Federal Non-recognition Complicates State Income Taxation of Same-Sex Relationships, 24 Colum. J. Gender & L. 29, 33 (2012).) This also ignores the fact that different-sex couples (who are eligible to enter into a Colorado civil union) are apparently (at least according to the IRS) eligible to file joint federal income tax returns so long as their relationship is the legal equivalent of marriage. But will different-sex parties to a Colorado civil union now be allowed to file a joint federal return if their relationship is something less than a marriage? What about same-sex parties to a Colorado civil union if the U.S. Supreme Court decides to strike down section 3 of DOMA?