From the Wall Street Journal’s article Gay Couples Get Equal Tax Treatment:
The Internal Revenue Service has ruled that same-sex couples must be treated the same as heterosexual couples under a feature of California tax law. Advocates for the change say it is the first time the agency has acknowledged gay couples as a unit for tax purposes.
The change reverses a 2006 IRS ruling and opens a tax benefit to many same-sex couples that wasn’t available before. It may affect couples in Nevada and Washington state, as well.
Specifically, the agency said nearly 58,000 couples who are registered as domestic partners in California must combine their income and each report half of it on their separate tax returns. Same-sex couples account for an estimated 95% of the state’s domestic partnerships; partnership status is also available to heterosexual couples in which one partner is over age 62.
