The Supreme Court on Monday upheld an Indiana law requiring voters to show photo identification at polling places, a decision that drew mixed responses from lawmakers and outside experts — and likely will spawn many more court challenges.

In a 6-3 decision, Associate Justice John Paul Stevens wrote that Indiana’s ID law is not a “substantial burden,” given that the state identification cards are free and obtaining them does not “represent a significant increase over the usual burden of voting.”

In deciding the combined case, Crawford v. Marion County Election Board, Stevens was joined by Chief Justice John Roberts and Justices Antonin Scalia, Anthony Kennedy, Clarence Thomas and Samuel Alito.

“There is no question about the legitimacy or importance of the state’s interest in counting only the votes of eligible voters,” Stevens wrote for himself, Roberts and Kennedy. “While the most effective method of preventing election fraud may well be debatable, the propriety of doing so is perfectly clear.”

Justices David Souter, Ruth Bader Ginsberg and Stephen Breyer dissented. Writing for himself and Ginsberg, Souter agreed with many civil rights and watchdog groups that Indiana’s law “threatens to impose nontrivial burdens on the voting rights of tens of thousands of the state’s citizens.”

Indiana’s law requires that voters present a driver’s license or other official photo identification before they are allowed to vote. Registered voters without proper identification may cast provisional ballots, which are counted if proof of eligibility is presented in person to local election officials within 10 days.

The dissenting justices, many Democrats and other critics of the GOP-backed law argue that voter-identification statutes are little more than modern-day poll taxes that reduce Election Day turnout by elderly, low-income and minority voters — voters who tend to pick Democrats.

“The need to travel to a [license branch] will affect voters according to their circumstances, with the average person probably viewing it as nothing more than an inconvenience,” Souter wrote. “Poor, old and disabled voters who do not drive a car, however, many find the trip prohibitive, witness to the fact the [Indiana Bureau of Motor Vehicles] has far fewer license branches in each county than there are voting precincts.”

Rep. Robert Brady (D-Pa.), chairman of House Administration Committee, said Monday that the high court acted politically in upholding Indiana’s law, which “has the potential to severely disenfranchise minority and elderly voters as well as student voters, three demographics that have been historically targeted for voter suppression.”

“The members of the Supreme Court who endorsed this policy were all appointed under Republican administrations, further reinforcing the idea that suppressing broad voter participation serves conservative Republican interests,” Brady said in a statement.

But the high court’s majority, as well as many Republicans, argue that the potential for voter fraud without ID requirements far exceeds the likelihood that a typical voter in 2008 would not have some acceptable form of photo identification.

House Minority Whip Roy Blunt (R-Mo.), whose home state adopted a similar law that was thrown out in state court, said the Supreme Court “affirmed a principle the American people have overwhelmingly supported for some time: Asking citizens to produce a simple form of identification before voting is neither unreasonable nor unconstitutional — and if it helps impede voter fraud, absolutely necessary to ensure the basic integrity of the democratic process.”

“Only in a place like Washington, D.C., does it make sense that a valid photo ID should be required to board an airplane, enter a federal building, or swipe a debit card — but not to discharge one of our most sacred duties as citizens and most precious rights as Americans,” Blunt said in a statement.

Voter identification laws played a central role in the still-deadlocked nomination fight over GOP Federal Election Commission pick Hans von Spakovsky. The former Justice Department lawyer continues to be criticized by Senate Democrats for pushing similar requirements in Georgia and elsewhere while at Justice.

Von Spakovsky said on Monday that the high court’s decision backs up once-controversial decisions he made at the Justice Department.

“This decision not only confirms the validity of photo ID laws, but it completely vindicates the Bush Justice Department and refutes those critics who claimed that the Department somehow acted ‘improperly’ when it approved Georgia’s photo ID law in 2005,” he said in a statement.

But it seems unlikely that the Senate deadlock over FEC nominations will be eased following the Supreme Court’s ruling. And in fact it seems likely that more litigation over voting rights is inevitable.

The American Civil Liberties Union, which called the law “an unconstitutional burden on voting rights,” signaled that the high court’s decision could generate a slew of post-Election Day 2008 court cases.

“We are very disappointed in today’s decision, but it leaves the door open to future challenges in Indiana and elsewhere by registered voters who are denied their right to vote based on onerous and unconstitutional voter ID laws,” ACLU Legal Director Steven Shapiro said in a statement. “We should be seeking ways to encourage more people to vote, not inventing excuses to deny citizens their constitutional voting rights.”