FOR DECADES Virginia has allowed residents who lack proof of identification or whose IDs have been lost or stolen to vote, provided they are listed in the voting rolls and sign sworn statements attesting to their identities. Now, in response to no known problem, Republicans are backing a change already approved by the House of Delegates that would allow such citizens to cast only provisional ballots, which would be counted only if their identities were subsequently verified with IDs. Given that 11 percent of voting-age citizens nationally lack photo IDs, that would place unmanageable burdens on thousands of would-be voters in the commonwealth.

The bill’s chief sponsor is Del. Mark R. Cole (R-Fredericksburg), whose previous claim to fame was a bill in 2010 banning employers from planting microchips in their workers, on the grounds that doing so might enable a surreptitious incursion by the antichrist. Yes, really.

Mr. Cole says that his voting legislation would prevent voter fraud — specifically, ballots cast by impersonators. However, in an e-mail exchange with us on the subject, he did not respond when asked to name a single instance of such fraud in Virginia. Nor could he provide evidence when questioned directly by Democratic lawmakers in committee. In fact, he admitted, he knew of no instances.

A 2006 study by the Brennan Center for Justice at New York University, which supports voting rights, found that 21 million people, or 11 percent of American citizens, lack government-issued photo IDs such as driver’s licenses and millions more women have only out-of-date IDs with their maiden names.

The percentage of voting-age citizens lacking IDs was significantly higher among African Americans (25 percent); among people aged 65 or older (18 percent); and among low-income Americans (15 percent).

So the effect of Mr. Cole’s legislation would be to disenfranchise voters who helped Democrats, including President Obama, get elected in Virginia. If it survives a vote in the Senate, we hope it will be vetoed by Gov. Robert F. McDonnell (R).

If it does become law, Virginia risks a challenge by the Justice Department, which may review any changes in the state’s voting rules under the 1965 Voting Rights Act.

Just over a year ago, Virginia Attorney General Ken Cuccinelli II said that Virginia, one of nine states covered by the law, had outgrown its history of institutional racism and should be released from Justice Department oversight. Legislation such as Mr. Cole’s undermines that argument.