Democrats who are challenging the law say it uses prevention of fraud as a pretext to discourage elderly, poor and minority voters — those most likely to lack proper ID and who tend to vote for Democrats.
Opponents say there have been no Indiana prosecutions of in-person voter fraud — the kind the law is supposed to prevent.
A federal judge who upheld the voter ID law pointed out that opponents were unable to produce evidence of a single, individual Indiana resident who had been barred from voting because of the law.
Courts have upheld voter ID laws in Arizona, Georgia and Michigan, but struck down Missouri's. Wednesday's case should be decided by late June, in time for the November 2008 elections.
The justices could use the case to instruct courts on how to weigh claims of voter fraud versus those of disenfranchisement.
The Supreme Court was bitterly divided, 5-4, in 2000 in Bush v. Gore, the case that clinched the presidential election for George W. Bush.
The consolidated cases are Crawford v. Marion County Election Board, 07-21, and Indiana Democratic Party v. Rokita, 07-25.