Oklahoma's health department refused to issue a birth certificate to a child with "two fathers."
Two-year-old Vivian has been under the care of Gregory Hampel and Edmund Swaya, in Seattle, Wash., since shortly after she was born in Oklahoma, reports the website Gay365.com
The homosexual-rights group Lambda Legal is arguing Oklahoma law allows for co-adoption.
"The Health Department does not have authority to decide who gets a birth certificate or who is a legal parent," said Brian Chase, staff attorney for Lambda Legal.
Chase said it's "both unlawful and unconscionable to withhold this vital document because of anti-gay prejudice against a child's parents."
Oklahoma State Attorney General W.A. Drew Edmonson recently issued an advisory stating that under the federal Constitution and Oklahoma laws, the state must issue birth certificates for children legally adopted outside of Oklahoma, including to children adopted by same-sex couples, the website said.
Lambda Legal won a similar case for a lesbian couple in Vermont who adopted a baby from Mississippi.
A state judge ordered the state Board of Health to issue a certificate listing both mothers.