The law has become a major flashpoint between Democrats and Republicans, with both sides claiming they're looking out for the best interests of voters.
Under the Indiana law, registered voters must present a government-issued photo ID - such as a driver's license - to take part in the elections. Voters without the proper identification can cast provisional ballots, but those count only if the voter shows a photo ID at a county election office within 10 days.
Republicans championed the Indiana effort, as well as similar laws in Georgia, Florida and Missouri (although Missouri's was struck down). If the high court strikes down Indiana's law, the other laws could be in jeopardy as well. The Republicans backing such measures say they're trying to reduce fraud and restore voter confidence in elections, especially after the disputed 2000 presidential election.
"Vote fraud is not a victimless crime. It diminishes and marginalizes the vote of every eligible voter who takes the time and effort to vote, and it undermines the legitimacy of the entire election process," lawyers for the Republican National Committee wrote in a high court brief.
They say that showing a photo ID is a common part of modern life. People often need IDs to get new jobs, board airplanes, enter courthouses, buy alcohol or rent movies, they point out.
But Democrats argue that the laws are addressing a type of fraud that rarely, if ever, occurs. Individual voters don't often pose as other people in order to change the outcome of elections. Other voting shenanigans - such as stuffing ballot boxes, paying for votes or coercing people with absentee ballots - is much more common, they say.
"No one has ever been prosecuted for in-person voter fraud in Indiana's history. Nor has anyone ever cited a single episode of such fraud occurring in the state," attorneys for the Indiana Democratic Party wrote in a high court brief.
Instead, Democrats say the GOP initiatives are designed to turn away elderly and minority voters who are less likely to have valid IDs and who tend to vote for Democrats.
Republicans passed the measure shortly after taking control of the Indiana House of Representatives and the governor's office in 2005. It passed on party-line votes.
When the Indiana Democratic Party challenged the law in federal court, judges appointed by Republican presidents upheld it at both the trial and appellate levels. In the appeals court, though, a judge named by a Democratic president issued a caustic dissent.
Now that the measure is before the high court, eight GOP state attorneys general came together to support the law in a friend-of-the-court brief. Democratic secretaries of state from three states filed an opposing friend-of-the-court brief.
In deciding the case, the justices will likely have to determine how closely courts should scrutinize laws that could prevent people from voting.
Those challenging the law, the Indiana Democratic Party and the American Civil Liberties Union, say lawmakers must have a good reason for making it harder to vote or preventing some people from voting altogether. The Democratic secretaries of state who took the challengers' side are from Missouri, Ohio and Vermont; they were joined by former secretaries from Georgia and Maryland.
The fact that Republicans focused on changes that would disproportionately affect Democratic voters should make courts especially wary of the law, they argued.
But Republicans say judges should let legislators determine the rules for holding elections. They say lawmakers don't have to wait for a problem to occur in order to address it. Legislators can pass laws to prevent the problem in the first place, they argue.
"Every regulation on voting necessarily imposes some burden on voters," wrote the GOP attorneys general. The Republican state attorneys general in the friend-of-the-court brief hail from Texas, Alabama, Colorado, Florida, Hawaii, Michigan, Nebraska and South Dakota. Georgia Secretary of State Karen Handel (R) filed a separate brief backing the law.
Common election practices already limit voter access to the polls, such as requiring voters to register beforehand, holding elections on Tuesdays and limiting the number of polling places and the hours they are open, the attorneys general explained.
The debate in state capitols comes after Congress passed the Help America Vote Act in 2002. The federal law requires first-time voters who register by mail without accompanying documentation to show identification before they vote.
Republican backers of the voter identification laws say they are similar to proposals outlined by an electoral reform commission headed by former President Jimmy Carter and former U.S. Secretary of State James Baker.
The group recommended in 2005 that states require voters to present government-issued identification, but it also called for a long phase-in period and aggressive efforts to get IDs to people without them. As the commission recommended, Indiana allows poor voters to get photo IDs for free, but they may need to obtain birth certificates first, which can cost money.