State officials across the South are aggressively moving ahead with new laws requiring voters to show photo identification at the polls after the Supreme Court decision striking down a portion of the Voting Rights Act.

The Republicans who control state legislatures throughout the region say such laws are needed to prevent voter fraud. But such fraud is extremely rare, and Democrats are concerned that the proposed changes will make it harder for many poor voters and members of minorities — who tend to vote Democratic — to cast their ballots in states that once discriminated against black voters with poll taxes and literacy tests.

The Supreme Court ruling last month freed a number of states with a history of discrimination, mostly in the South, of the requirement to get advance federal permission in order to make changes to their election laws.

Within hours, Texas officials said that they would begin enforcing a strict photo identification requirement for voters, which had been blocked by a federal court on the ground that it would disproportionately affect black and Hispanic voters. In Mississippi and Alabama, which had passed their own voter identification laws but had not received federal approval for them, state officials said that they were moving to begin enforcing the laws.