In a speech to Campus Progress' annual conference in Washington, Clinton compared efforts to change voting laws to those in the South during the Jim Crow era, CNN reported.
"There has never been in my lifetime, since we got rid of the poll tax and all the voter Jim Crow burdens on voting, the determined effort to limit a franchise that we see today," he said.
Examples Clinton brought up include Gov. Rick Scott's bid to reverse a Florida law allowing ex-convicts to vote once they are off probation and a plan in New Hampshire to bar students from registering to vote at their college addresses.
In 2008, the number of younger voters, many of them supporters of then-Sen. Barack Obama, was at an all-time high. The youth vote dropped sharply in 2010 when Republicans regained a majority in the House.
"They are trying to make the 2012 electorate look more like the 2010 electorate than the 2008 electorate," Clinton said. "Are you fighting? You should be fighting it."