May a state government impose a restriction on voting that will keep tens of thousands of eligible voters, especially African-American and Latino citizens, from casting ballots without any evidence that this is necessary to prevent fraud? The answer should be clear that such a limit is unconstitutional.

Unfortunately, the Supreme Court's ruling on Monday upholding a requirement for photo identification in order to vote is likely to lead to a wave of laws across the country that will disenfranchise countless voters. Even worse, the Supreme Court said it does not matter if the restrictions are motivated by partisan politics and the desire of one political party to discourage votes for the other.

At issue before the Supreme Court was an Indiana law requiring photo identification in order to vote. At first, this may seem innocuous, but in operation it is quite insidious.

The Indiana legislature adopted the requirement with every Republican legislator voting for it and every Democrat voting against it. They knew statistics consistently show that such a law has a far greater effect on those likely to vote Democratic, especially African Americans and Latinos. The reality is there are many individuals who do not have photo identification and these tend to be the poorest in society, often citizens of color.

It is estimated that, at a minimum, 43,000 eligible voters in Indiana will be denied the ability to vote because they lack photo identification. This might be justified if there were a serious voter fraud problem in Indiana and there was no other way to solve it. But as Justice David Souter noted in his dissenting opinion, there is not "a shred of evidence that in-person voter impersonation is a problem in the state."

Justice John Paul Stevens, in an opinion joined by Chief Justice John Roberts and Justice Anthony Kennedy, engaged in a balancing test, concluding the state had a legitimate interest in preventing fraud and the burden on voting was minimal because individuals could easily obtain photo identification. Justice Antonin Scalia, joined by Justices Clarence Thomas and Samuel Alito, went even further, saying that a requirement for voting, even if it keeps some from voting, is allowed unless it has a "severe" impact on voting.

The flaw in these justices' reasoning is it ignores the fundamental nature of the right to vote. Under traditional principles of constitutional law, the government may burden a fundamental right only if its action is necessary to achieve a compelling interest. The balancing test used by Justice Stevens and the extreme deference advanced by Justice Scalia is inconsistent with the need for the government to prove that its restrictions on a fundamental right are truly essential. Justice Stevens said the challengers had to meet a "heavy burden" to have the law invalidated. But when a fundamental right is involved, the burden is always on the government to show that the law is needed.

For example, more than 40 years ago, the Supreme Court invalidated a Virginia law that imposed a poll tax of $1. The tax was intended mainly to discourage blacks from voting. The court was explicit that any restriction that would keep some citizens from voting could be tolerated only to achieve interests of the greatest importance. Under Justice Scalia's approach, such poll taxes would be allowed because they apply to everyone and do not have a "severe" effect on voting.

Unfortunately, today's Supreme Court gave no weight whatsoever to the partisan context of Indiana's law and others like it. There was no dispute that Republicans saw this law as a way of lessening votes for Democrats. But Justice Stevens said this did not matter.

This is an open invitation to state legislatures across the country to devise requirements for voting that keep members of the other political party from being able to vote. So long as legislators assert their goal is preventing fraud, even when there is no evidence to support it, Monday's decision will require that such laws be upheld.

Long ago, the Supreme Court proclaimed the right to vote is the most basic of all liberties because it preserves all other rights. It is this right that distinguishes a democracy from all other forms of government.

Although the government certainly has a vital interest in preventing fraud, more than a mere assertion of the interest should be required before tens of thousands are denied the right to vote. The Supreme Court's decision, and what it portends, is a major setback for fairness and equality in voting -- and for American democracy.