A federal law stated that a child born out of wedlock in a foreign country to an American mother was automatically a United States citizen. However, the law stated that a child born out of wedlock in a foreign country to an American father was not automatically a United States citizen. Under the latter situation, the law provided that the child could become a citizen if the father established paternity before the child turned 18. Tuan Anh Nguyen (defendant) was born in Vietnam to a Vietnamese mother and an American father, Joseph Boulais. Nguyen became a permanent resident of the United States when he was six years old. At 22, Nguyen pled guilty to sexual assault on a minor. The Immigration and Naturalization Service (INS) (plaintiff) commenced deportation proceedings. Boulais did not establish that he was Nguyen’s father until Nguyen was 28. Nguyen and Boulais claimed that the federal citizenship law was unconstitutional because it denied fathers the equal protection of the laws. The United States Supreme Court granted certiorari.