The Charles County town of La Plata, perhaps best known as the epicenter of a tornado, could become the eye of a voting rights storm because it requires residents to show identification to cast ballots in local elections.

The American Civil Liberties Union, joined by the NAACP, considers the practice a "violation of the fundamental right to vote" in Maryland. The groups are asking La Plata -- the county seat with a population of 9,000 -- to repeal the identification requirement, and the ACLU has suggested it might pursue legal action if the town does not comply.

Twenty-two states, including Virginia, require proof of identification on Election Day. Maryland does not, and La Plata appears to be unusual -- if not unique -- among the state's cities and towns, according to the ACLU and interviews with a sampling of election officials in Rockville, Annapolis, Bowie and Leonardtown.

Doug Miller, La Plata's town manager, said the Town Council would review the issue sometime before the next election, in spring 2007. He defended the practice, which has been in effect for more than two decades.

"Obviously, we want you to prove that you are who you say you are to prevent voter fraud," Miller said in an interview last week.

ACLU staff attorney David Rocah and the NAACP said the state constitution does not allow counties or municipalities to add to the state's registration requirements.

The issue of identification has become part of a partisan debate since voting irregularities were reported in the 2000 presidential election. Federal legislation in 2002 required all states to ask for identification from first-time voters who registered by mail and did not provide acceptable documentation.

Many Democrats see it as restrictive and intimidating, particularly to minorities and the elderly. But many Republicans see it as necessary to curb voter fraud.

"I'm not sure that either side makes a compelling argument," said Dan Seligson, editor of the nonpartisan Web site, which tracks and analyzes election legislation.

Seligson said he has not seen evidence of a drop-off in voting in states that have adopted identification requirements. And, he said, such laws do not prevent what appears to be the more common form of voter fraud, which is carried out through the mail.

Still, the debate continues. Last month, a U.S. appeals court upheld an injunction blocking Georgia from enforcing one of the country's toughest identification laws, which required voters to produce government-issued identification at the polls.

Del. Donald H. Dwyer Jr. (R-Anne Arundel) said he plans to introduce legislation for a third time in January that would require all Maryland voters to show identification at the polls.

"Law-abiding citizens don't have any issue with presenting their ID to vote," said Dwyer, whose bill did not make it out of committee last session in the Democrat-controlled House of Delegates. "If someone is offended, I would be suspect as to whether that person is who they claim to be."

The controversy in La Plata began in May after the town's mayoral and council elections, in which a record 1,153 people voted. Catherine Stevens, a part-time lawyer who teaches at the College of Southern Maryland, said she was surprised to see a sign on the front door of the polling place that asked residents to have identification ready to show the election judge.

"I was afraid people who didn't have ID would just turn around before they got inside," she said.

Stevens presented her driver's license and voted without incident. She called the ACLU because, she said, "I don't think it's constitutional."

The ACLU of Maryland agreed, and leaders of the local NAACP branch last week joined the call for repealing the requirement during a legislative forum with Charles County commissioners and state legislators.

La Plata's attorney, Frederick Sussman, told the ACLU in a September letter that the requirement "did not have a chilling effect on any person's right to cast a ballot" and is "less intrusive and more respective of voters' privacy interests than the state mandates."

In federal, state and county elections in Maryland, election judges are supposed to ask for a voter's name, address and month and day of birth. In La Plata's municipal elections, voters are required under the town code to present identification with "a signature or picture and an address or a combination of any of these."

Sussman said he would meet with the mayor and council to "determine what changes, if any, should be made."

"While the issue raised in your letter is important," he wrote, "the matter is not one of great urgency" because the next election is scheduled for 2007.

It is uncertain what prompted La Plata's leaders to adopt an identification requirement in 1981. The mayor at the time, Victor Bowling, said he did not have an exact recollection. He remembered a discussion about how to clear up confusion for residents who had a La Plata mailing address but did not reside within the town limits and therefore could not vote in municipal elections.

Whatever the reasons, opponents of the identification requirement say the language in the La Plata code effectively means that voters must show a driver's license, U.S. passport or state ID card -- all documents that cost money.

"It's hard for some people to understand or believe, but there are some people who don't drive or travel overseas," said Rocah, the ACLU attorney.

As for what's next, he said, "if they are going to repeal it, good. If they're not, then we're going to decide how to proceed. There is a clear policy choice for them to decide."