Proponents of Wisconsin's voter identification law hit a roadblock Tuesday as a federal judge struck down and invalidated the law on the grounds that it would have a disproportionate effect on the poor and minorities.

U.S. District Judge Lynn Adelman issued his long-awaited decision Tuesday. It invalidates Wisconsin's law. Wisconsin's law would have required voters to show a state-issued photo ID at the polls. Supporters said it would cut down on voter fraud and boost public confidence in the integrity of the election process. But Adelman sided with opponents, who said it disproportionately excluded poor and minority voters because they're less likely to have photo IDs or the documents needed to get them.

Wisconsin's voter identification law was one of the toughest in the nation, but the state issued free identification cards to those lacking an acceptable photo ID card.

Voter ID has become a hotly-contested issue, with many states pointing to evidence that their voter roles may have issues with integrity. Proponents of voter ID say that requiring an identification card would solve the majority of these issues.