Washington (CNN) A same-sex American couple whose daughter was denied birthright citizenship filed suit against the State Department on Thursday, joining a growing list of LGBTQ families turning to litigation to combat the policy.

Although Roee and Adiel Kiviti are both US citizens, as is their almost three-year-old son Lev, their six-month-old daughter Kessem was not granted birthright citizenship due to a State Department policy that considers her "born out of wedlock." The Kivitis said they received official notice of the rejection in early July.

Roee Kiviti told CNN in a phone interview Thursday that even though they had been told by the passport agency to expected a rejection, "getting the letter in the mail, in writing so we can see this discriminatory policy was really just a punch in the gut."

"We knew that we had to act for our daughter, for our family, for other families so they don't have to deal with this," he said.

The lawsuit was filed in the US District Court of Maryland by Immigration Equality, Lambda Legal, and pro bono counsel Morgan Lewis. Asked for comment, a State Department official said they do not comment on pending litigation.

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