Ever since twins Aiden and Ethan Dvash-Banks were born in Toronto in September 2016, they have shared everything—the same button nose, the same swoopy haircut, the same pug/terrier mix London. But for years, the U.S. State Department has fought an escalating legal battle to ensure that they don’t share one important thing: American citizenship.

Although Aiden and Ethan’s fathers, Andrew and Elad Dvash-Banks, have been married since 2010, only Andrew is an American citizen. While that would be enough for children in a heterosexual marriage to qualify for U.S. citizenship while born abroad, the State Department has held the Dvash-Bankses to a different standard, requiring the family to undergo DNA testing to establish that Aiden—but not Ethan—was the biological son of a U.S. citizen.

The boys’ parents sued, arguing in federal court that proving a biological connection between a child and a U.S. citizen parent isn’t required to extend birthright citizenship from a married parent to a child, and in February, the judge ruled in their favor.

“The basis for the State Department’s imposition of a biological requirement is its strained interpretation” of existing immigration law, U.S. District Judge John F. Walter wrote in a decision issued in February, dismissing the department’s attempts to institute a biological testing standard for the children of binational married couples “unilateral.”

But on Monday, the State Department appealed that decision, continuing a years-long bid to strip Ethan of his citizenship.

“Once again, the State Department is refusing to recognize Andrew and Elad’s rights as a married couple. The government’s decision to try to strip Ethan of his citizenship is unconstitutional, discriminatory, and morally reprehensible,” said Aaron C. Morris, executive director of Immigration Equality, a nonprofit that advocates for LGBT people in the immigration system. Morris successfully argued in federal court that a policy requiring genetic testing for the children of same-sex binational couples created a new double standard for citizenship: one for the children of gay couples and one for the children of straight couples.

After the Supreme Court struck down a ban on federal recognition of same-sex marriage in 2013, the Department of Homeland Security issued a guidance declaring that “just as [U.S. Citizenship and Immigration Services] applies all relevant laws to determine the validity of an opposite-sex marriage, we will apply all relevant laws to determine the validity of a same-sex marriage.”

In response to a request for comment on the appeal, and on whether it plans to require DNA testing of all binational married couples in order to establish a biological relationship and thereby to establish birthright citizenship, a State Department spokesperson said that the department “does not comment on pending litigation.”

Morris also noted that in the Ninth Circuit Court of Appeals, where the State Department has filed its appeal, the standard of using DNA testing to ensure a biological relationship between a child and a married U.S. citizen parent in order to confer citizenship has already been soundly rejected.

“This is settled law in the Ninth Circuit, which has already established that citizenship may pass from a married parent to a child regardless of whether or not they have a biological relationship,” Morris said.

Despite that precedent, Aiden and Ethan’s fathers are still deeply concerned with the State Department’s decision to appeal the case.

“We’re outraged that the State Department is so intent on harming our family and the LGBTQ community,” Andrew and Elad said in a statement. “The fight is not over, and we will not rest until our family is treated fairly and equally. Nothing can tear us apart. The four of us are unbreakable.”