Nine state attorneys general, including Colorado’s Phil Weiser, asked a federal appeals court on Wednesday to allow an intersex Colorado resident to get a passport listing the person’s gender as nonbinary instead of male or female.

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 U.S. 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 Colorado as well as California, 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.

“Coloradans use state-issued identification documents every day to interact with government agencies, law enforcement, and businesses,” Weiser said in a statement Wednesday.

“Providing non-binary identification documents in our state is easy to manage, respects our citizens’ gender identity, and is the right thing to do,” he said. “The federal government needs to catch up with the states that are leading the way when it comes to equality. All Americans should be able to obtain a passport that accurately reflects their gender.”

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.”

LGBTQ advocacy group One Colorado issued a statement Wednesday in response to the multistate brief.

“Colorado is leading the way with states like California and Oregon by offering a third gender option that is neither male nor female on a suite of state-issued identity documents, like birth certificates, driver’s licenses, and state identification cards,” One Colorado Executive Director Daniel Ramos said in the statement. “The recent passage of House Bill 19-1039: Jude’s Law and its strong bipartisan support demonstrates that ensuring transgender and non-binary Coloradans have access to identity documents that reflect their authentic selves is truly a nonpartisan issue. It is time for our federal government to follow suit and offer non-binary gender options on federal identity documents.”

House Bill 1039, which passed the Colorado legislature in April, allows transgender Coloradans to obtain new birth certificates instead of amended ones. The bill is known as “Jude’s Law” for a transgender girl who testified on the bill for the past four years.

The Associated Press and Colorado Politics contributed.