The U.S. Supreme Court case Ruben Flores-Villar v. United States in 2010 revolved around the issue of citizenship and gender discrimination. The petitioner, Ruben Flores-Villar, was born in Mexico to an American father and a Mexican mother who were not married at the time of his birth. He moved to the U.S with his father during childhood but never obtained formal recognition as a citizen from immigration authorities. Later on, he faced deportation after criminal convictions which led him to challenge the constitutionality of laws governing citizenship for children born abroad out-of-wedlock to mixed-nationality parents. Flores-Villar argued that these laws unfairly discriminated against fathers because they required unwed U.S.-citizen fathers (but not mothers) living abroad to have lived in America for five years after their fourteenth birthday before they could pass on citizenship automatically at birth; whereas unwed U.S-citizen mothers only needed one year residency prior to childbirth. However, by an equally divided court (4-4), due Justice Elena Kagan's recusal from this case having worked on it while she served as Solicitor General under President Obama’s administration -the Ninth Circuit ruling stood without setting any national precedent: meaning that Flores-Villar's claim was rejected and he remained subject for deportation.

In the dissenting opinion for Ruben Flores-Villar v. United States, Justice Ginsburg disagreed with the majority's decision to uphold a law that imposed different residency requirements on U.S. citizen mothers and fathers seeking citizenship for their children born abroad out of wedlock. She argued that this law was based on outdated stereotypes about gender roles in parenting, which violated equal protection principles under the Fifth Amendment's Due Process Clause. Specifically, she criticized the assumption that unwed mothers are naturally more connected to their children than unwed fathers, calling it an "enduring stereotype" without basis in modern understanding or reality. Furthermore, she contended that such differential treatment had no substantial relation to any important governmental interest and thus failed intermediate scrutiny review.