Registered domestic partners may not file a federal return using a married filing separately or jointly filing status. Registered domestic partners are not married under state law. Therefore, these taxpayers are not married for federal tax purposes.
How you handle state tax forms depends on which community property state you call home.
https://www.irs.gov/newsroom/answers-to-frequently-asked-questions-for-registered-domestic-partners-...
Tax Tips for Registered Domestic Partners and Unmarried Same Sex Couples in Community Property State...
