If DOMA is repealed or ruled unconstitutional, then same-sex marriages will have to be given the same effect as opposite sex marriages. But what about registered same sex couples in those states that recognize the relationship as a marital equivalent, but don’t call it marriage?

There are nine such states: California, Delaware, Hawaii, Illinois, Nevada, New Jersey, Oregon, Rhode Island, and Washington (plus the District of Columbia). Right now a number of those states offer these alternative relationships to partners of opposite sex as well as to partners of the same sex. Some states (e.g, California and Washington) recognize some opposite sex registered couples as RDPs (one partner must be age 62 or older). Some states (e.g, Hawaii and Illinois) allow all opposite sex couples who want to enter into a civil union to do so. (See also Nevada rules on RDPs).

Most of us who have been following these changes have assumed that RDP status and civil union status, which both fall short of full marriage, do not create marriages that will be recognized by federal tax laws. We thought this rule was the law independent of DOMA. That is, an opposite sex RDP couple in California, unaffected by DOMA which only applies to same-sex spouses, would nonetheless probably be treated as unmarried because under state law they are not in fact married. In fact, that is one reason opposite sex couples might elect RDP or civil union status rather than marriage—to be treated as unmarried at the federal level (for tax, social security, and Medicaid purposes) even though they receive all the state law benefits of marriage.

Personally, I have always thought this view of the matter was wrong. If you are treated the same as spouses no matter what you are called you probably ought to be treated as spouses at the federal level as well. But, nonetheless, the common wisdom seems to have been otherwise.

However, in a recent letter from the Office of Chief Counsel, IRS, in response to a query about opposite sex civil union partners in Illinois, the IRS appears to be taking a different position. The letter concludes that if state law treats you as husband and wife you should also be treated as husband and wife for purposes of filing a joint return at the federal level. The letter only addresses the joint return filing question. And, of course, it is not authority. But it is interesting to learn that the Commissioner has responded to the question, through a letter out of Chief Counsel’s office, that concludes that a status that is the equivalent of marriage should be treated as marriage for federal tax law purposes.

I suspect that will come as news to many folks. If the conclusion holds, then that would mean that once DOMA falls, RDPs and civil union partners will also be treated as “husbands and wives” under federal tax law.

For a full version of the letter click here.