At issue in the case is the "pre-clearance" provision of the Voting Rights Act, § 5. The VRA as a whole forbids states from discriminating by race in any feature of their voting and election systems -- ranging all the way from registration procedures for individual voters to the system of congressional and legislative districts states draw for elections. Racial discrimination in voting is barred by the Fifteenth Amendment; § 2 of the amendment states that "Congress shall have power to enforce this article by appropriate legislation."

Under the VRA, if a state changes its election laws, any group of voters that believes it has been disadvantaged by a change can bring suit in federal court to block the change. The act was passed in 1965, however, a time when much of the South and parts of the Southwest in essence maintained apartheid voting systems. These systems excluded non-white voters, using discriminatory registration rules and deliberate gerrymanders in districting. It might have taken decades to dismantle that system by individual lawsuits. To confront the scale of the problem, the VRA designated some states and parts of states as "covered jurisdictions." (The designation was based on the percentage of minority voters who actually got to cast votes in the election of 1964; later, a few jurisdictions were added based on percentage of voters in 1972.)

Because of their history, the "covered jurisdictions" are placed under a special rule. Before they can make any change in their systems, they must obtain "pre-clearance" from the federal government. The state, in essence, has to prove that its new election rule, whatever it is, will not cause non-white voters to lose access to or influence in the election system. Individuals can still sue; but the change also has to go through scrutiny at the federal level whether there is a suit or not. That "pre-clearance" can be granted in two ways: A state can apply to the Justice Department for "administrative pre-clearance"; or, if it chooses, it can bring suit in the District Court for the District of Columbia. In either case, the state has to prove its new change would not harm minority voters.

The Voting Rights Act is one of the greatest success stories in the history of American civil rights law. Within a few years, barriers to the ballot tumbled in states across the South and West. The old elite of the Jim Crow South fought on; but the "pre-clearance" procedure stymied its attempts to neutralize political gains with new district lines, registration rules, or practices at the polling place. The freer political atmosphere in the South meant the growth of a two-party system and bi-racial House delegations. Four times, Congress has reauthorized the VRA, most recently in 2006, by a vote of 390 to 33 in the House, and 98 to 0 in the Senate.