The ACLU has posted this press release and this letter. The release begins:

In an April 14, 2006, letter to the U.S. Department of Justice, the ACLU cited data from a 2005 Florida study showing the retrogressive effect of photo ID requirements on black and Hispanic voters. Specifically, the data shows that black voters in Hillsborough County, Florida, were three times as likely as white non-Hispanic voters to use affidavits to prove their identities at the precinct level and Hispanic voters were twice as likely to use affidavits. In Hendry County, black voters were three times as likely as white non-Hispanics to use affidavits and Hispanic voters were slightly more likely to use affidavits.”