In the 1964 case Louisiana et al. v. United States, the U.S Supreme Court ruled against a Louisiana law that required voters to prove they could read and write any section of the Constitution in English and demonstrate an understanding of it before being allowed to vote. The court held that this literacy test was unconstitutional because it violated the Fifteenth Amendment which prohibits racial discrimination in voting rights. The state argued that these tests were necessary for maintaining an educated electorate but failed to provide evidence showing how such requirements served a compelling state interest or why less discriminatory alternatives would not suffice. Furthermore, historical context suggested these laws disproportionately affected African American citizens due to systemic educational disparities caused by segregation policies, thus violating their constitutional right to equal protection under law as well as their voting rights.

In the dissenting opinion for Louisiana et al. v. United States, Justice Harlan argued that the majority's decision to strike down a Louisiana law requiring voters to interpret parts of the state constitution as a prerequisite for voting was an overreach of federal power. He contended that it is within states' rights to determine voter qualifications and this includes literacy tests or interpretation requirements, provided they are applied equally among all races and ethnicities. Furthermore, he believed there was insufficient evidence proving these requirements were used discriminatorily against African Americans in Louisiana specifically. Thus, he disagreed with the majority's view that such laws inherently violated Fifteenth Amendment protections against racial discrimination in voting rights.