KANSAS CITY, Kan. (AP) — A Kansas couple has filed a lawsuit in hopes of reversing federal immigration officials' decision not to allow their adopted Korean-born daughter to become a U.S. citizen.

Army veteran Patrick Schreiber and his wife finalized their niece's adoption in 2014 when she was 17, The Kansas City Star reported. She now studies at the University of Kansas but may soon be forced to leave the country when her visa expires.

Schreiber said an adoption attorney informed him he had until his niece turned 18 to adopt her. But a federal statute says children brought into the country must be adopted before age 16 for access to U.S. citizenship.

"The law clearly says that if you're 16 or older when adopted, you cannot derive citizenship from your parents," said USCIS spokeswoman Sharon Rummery. "We don't make the law. That's the job of Congress."

The girl arrived legally in the U.S. with a student visa at the age of 15 after family problems in Korea prompted the Schreibers to host her in 2012. Schreiber said he and wife put their niece's adoption on hold after the military called him to Afghanistan in 2013.

"I should have put my family ahead of the Army," Schreiber said.

Now Schreiber is determined to keep his family together, even if it means moving back to South Korea.

"Yes, she loves the United States. But our biggest concern is staying together as a family," Schreiber said.

The Schreibers' attorney, Rekha Sharma-Crawford, said the immigration system "really is broken."