(CNBC) — Same-sex couples in Washington state rushed giddily to the courthouse earlier this month after Washington became one of three states where voters approved laws giving them the legal right to marry.

Those newlyweds will probably be less excited the first time they get to file their tax returns together.

The gap between state laws that recognize same-sex marriage, and federal laws that don’t, makes tax season complicated at best, and costly at worst, for same-sex spouses.

“It’s certainly a big headache for people. I’ve literally seen them reduced to tears,” said M.V. Lee Badgett, research director of the Williams Institute for Sexual Orientation Law and Public Policy at the University of California, Los Angeles.

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