The states filed a brief with the 10th Circuit Court of Appeals in Denver asking the justices to uphold a lower court ruling that said the State Department could not deny a passport to Dana Zzyym.
Zzyym wanted a passport marked "X'' for gender, instead of "M'' or "F." Zzyym was born with ambiguous physical sexual characteristics and identifies as nonbinary in gender.
The State Department refused Zzyym's application, saying it would be hard to verify identities of nonbinary people and check their eligibility in government databases.
Zzyym sued in 2015, and a U.S. district judge in Denver rejected the State Department's reasoning. The department appealed.
The states filing the brief were California, Colorado, Maine, Minnesota, Nevada, New Jersey, Oregon, Vermont and Washington.
The states said they allow nonbinary gender designations on their driver's licenses and other documents, and it has not been complicated or a disruption. They said the State Department's refusal to recognize nonbinary gender would make it harder to verify someone's identity in government databases, not easier.
The International Civil Aviation organization, a U.N. agency that sets standards for international travel documents, says gender should be marked on passports as male, female or "X for unspecified."
Several countries issue passports with gender designations other than female or male, including "X'' or "O."
This story has been corrected to show the person's last name is Zzyym, not Zyymm.
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